Basics

Question 1

lst = ["a", "b", "c", "d", "e"]
lst[1:3]
lst[:4]
lst[3:]
del(lst[0])

Answer 1

lst = ["a", "b", "c", "d", "e"]
lst[1:3] --> ["b", "c"]
lst[:4] --> ["a", "b", "c", "d"]
lst[2:] --> ["c", "d", "e"]
del(lst[0]) --> lst = ["b", "c", "d", "e"]

Question 2

import numpy as np

Answer 2

arr = np.array([[1,2,3,4,5], [4,5,6,7,8]])
print (arr.shape)
--> (2, 5)
print (arr[0][2])
--> 3
print (arr[:, 1:3])
--> [[2, 3], [5,6]]
print (arr[1, :])
--> [4,5,6,7,8]

Question 3

arr = np.array([[1.27, 2.16, 3.32], [7.45, 6.12, 5.34]])
print (np.mean(arr[:,1]))
print (np.median(arr[:,1]))

Answer 3

arr = np.array([[1.27, 2.16, 3.32], [7.45, 6.12, 5.34]])
print (np.mean(arr[:,1])) –> 4.14
print (np.median(arr[:,1])) –> 4.14

Question 4

in ruby –> a = []
3.times{|x| 3.times{|y| a &laquo_space;[x,y] if x != y }}

a = (0..2).to_a.permutation(2).reject { |x| x[0] == x[1] }

–> [(0, 1), (0, 2), (1, 0), (1, 2), (2, 0), (2, 1)]

Answer 4

–> [(0, 1), (0, 2), (1, 0), (1, 2), (2, 0), (2, 1)]

in python --> a = []
 for x in range(3):
	for y in range(3):
	if x != y: 
		a += [(x,y)]

[(x,y) for x in xrange(3) for y in xrange(3) if x != y]

Question 5

print(count_vowels(‘aertewrweroe uerue eiiera gf’))

–> 15

Answer 5

print(count_vowels(‘aertewrweroe uerue eiiera gf’))

import re

def count_vowels(s = ''):
    if isinstance(s, str):
      return sum(1 for _ in re.finditer(r'[aeoui]', s))

return sum(1 for val in s if val in “aeouiAEOUI”)

Question 6

in ruby –> [(1,1), (2,4), (4,16)]

[1,2,3,4].select {|x| x != 3} . map! {|x| [x, x*x]}

Answer 6

in python –> [(1,1), (2,4), (4,16)]

[(x, x*x) for x in [1,2,3,4] if x != 3]

Question 7

disemvowel(“This website is for losers LOL!”),”Ths wbst s fr lsrs LL!”)

in ruby –>
def disemvowel(str)
str.chars.select {|v| v.match(/[^aeouiAEOUI]/) }.join
end

return str.gsub(/[aeouiAEOUI]/, ‘’)

Answer 7

disemvowel(“This website is for losers LOL!”),”Ths wbst s fr lsrs LL!”)

in python -->
import re
def disemvowel(string):
    re.sub(r'[aeouiAEOUI]', '', string)
    # re.sub(r'[aeoui]', '', string, flags=re.IGNORECASE)

return ““.join(c for c in string if c.lower() not in “aeoui”)

Question 8

is_square(-1)#, "Negative numbers cannot be square numbers")
(is_square( 3)
is_square( 4)
is_square(25)
is_square(86)

ruby –>
def is_square(n)
n < 0 ? false : Math.sqrt(n) % 1 == 0
end

Answer 8

is_square(-1)#, "Negative numbers cannot be square numbers")
(is_square( 3)
is_square( 4)
is_square(25)
is_square(86)

python -->
def is_square(n):
    n > 0 and (n**0.5).is_integer()

Question 9

print(make_int(“123”))
print(make_int(“00123”))
print(make_int(“1.23”))
print(make_int(“-123”))

Output

#123
#123
#-1
#-1

Answer 9

print(make_int(“123”))
print(make_int(“00123”))
print(make_int(“1.23”))
print(make_int(“-123”))

Output

#123
#123
#-1
#-1

using ternary operator for Python3

def make_int(string):
    return string.isdigit() and string or -1

Question 10

Tests

print(make_nametag(“Scott”, “Python”))
print(make_nametag(“Joe”, “games”))
print(make_nametag(“John”, “programming tips”))

Output

#Hi! My name is Scott. This lecture covers Python.
#Hi! My name is Joe. This lecture covers games.
#Hi! My name is John. This lecture covers programming tips.

Answer 10

Output

#Hi! My name is Scott. This lecture covers Python.
#Hi! My name is Joe. This lecture covers games.
#Hi! My name is John. This lecture covers programming tips.

def make_nametag(first_name, topic):
“””
Given two strings first_name and topic,
return a string of the form ““Hi! My name
is XXX. This lecture covers YYY.” where
XXX and YYY are first_name and topic.
“””
return (“Hi! My name is {}. This lecture covers {}.”).format(first_name, topic)

Question 11

Tests

example_string = “It’s just a flesh wound.”

print(is_substring(example_string, “just”))
print(is_substring(example_string, “flesh wound”))
print(is_substring(example_string, “piddog”))
print(is_substring(example_string, “it’s”))
print(is_substring(example_string, “It’s”))

Output

#True
#True
#False
#False
#True

Answer 11

Tests

example_string = “It’s just a flesh wound.”

print(is_substring(example_string, “just”))
print(is_substring(example_string, “flesh wound”))
print(is_substring(example_string, “piddog”))
print(is_substring(example_string, “it’s”))
print(is_substring(example_string, “It’s”))

Output

#True
#True
#False
#False
#True

is_substring(example_string, test_string):
return test_string in example_string

#return example_string.find(test_string) >= 0

Question 12

# Enter code here
primes = [2,3,5,7,11,13]

# Output
#3 7 13

Answer 12

# Enter code here
primes = [2,3,5,7,11,13]

# Output
#3 7 13

for i in range(1, len(primes), 2):
print(primes[i])

Question 13

count given word in text

print(word_count(“this pigdog is a fine pigdog”, “pigdog”))
print(word_count(“this pigdog is not a dog”, “dog”))
print(word_count(“this pigdog is not a pig”, “pigdog”))

# Output
#2
#1
#1

Answer 13

print(word_count(“this pigdog is a fine pigdog”, “pigdog”))
print(word_count(“this pigdog is not a dog”, “dog”))
print(word_count(“this pigdog is not a pig”, “pigdog”))

# Output
#2
#1
#1

def word_count(text, word):   
    return text.split().count(word)

Question 14

list(range(0,5))

Answer 14

list(range(0,5) –> [0,1,2,3,4]

Question 15

write a function which calculates the sum of the numbers in a list which are NOT divisible by 3)

print(strange_sum([1, 2, 3, 4, 5, 1, 2, 3, 4, 5]))
print(strange_sum(list(range(123)) + list(range(77))))

Answer 15

print(strange_sum([1, 2, 3, 4, 5, 1, 2, 3, 4, 5])) –> 24
print(strange_sum(list(range(123)) + list(range(77)))) –> 6994

def strange_sum(numbers):
  return sum([x for x in numbers if x % 3 != 0])

Question 16

lst = list(range(0,5)) --> [0,1,2,3,4]
lst2 = [11,12,13]
lst.insert(2, 10)
lst.extend(lst2)
lst.pop()
lst.pop(3)
lst.remove(0)
lst[1:3] = [0, 0, 0]

Answer 16

lst = list(range(0,5)) --> [0,1,2,3,4]
lst2 = [11,12,13]
lst.insert(2, 10) --> lst = [0,1,10,3,4]
lst.extend(lst2) --> lst = [0,1,10,3,4,11,12,13]
lst.pop() --> lst = [0,1,10,3,4,11,12]
lst.pop(3) --> lst = [0,1,10,4,11,12]
lst.remove(0) --> lst = [1,10,4,11,12]
lst[1:3] = [0, 0, 0] --> lst = [1, 0, 0, 0, 11, 12]

Question 17

Solution - Shuffle the items in a list

example_list = [2, 3, 5, 7, 11, 13]
print(example_list)

# Enter update code here
?
print(example_list)

#[2, 3, 5, 7, 11, 13]
#[11, 2, 7, 5, 13, 3]

Answer 17

import random

example_list = [2, 3, 5, 7, 11, 13]
print(example_list)

random.shuffle(example_list)
print(example_list)

#[2, 3, 5, 7, 11, 13]
#[11, 2, 7, 5, 13, 3]

Question 18

Template - Flatten a nested list

# Test code
print(flatten([]))
print(flatten([[]]))
print(flatten([[1, 2, 3]]))
print(flatten([["cat", "dog"], ["pig", "cow"]]))
print(flatten([[9, 8, 7], [6, 5], [4, 3, 2], [1]]))

# Output
#[]
#[]
#[1, 2, 3]
#['cat', 'dog', 'pig', 'cow']
#[9, 8, 7, 6, 5, 4, 3, 2, 1]

Answer 18

# Test code
print(flatten([]))
print(flatten([[]]))
print(flatten([[1, 2, 3]]))
print(flatten([["cat", "dog"], ["pig", "cow"]]))
print(flatten([[9, 8, 7], [6, 5], [4, 3, 2], [1]]))

# Output
#[]
#[]
#[1, 2, 3]
#['cat', 'dog', 'pig', 'cow']
#[9, 8, 7, 6, 5, 4, 3, 2, 1]

def flatten(nested_list):
     new = []
    for lst in nested_list:
        for i in range(len(lst)):
            new.append(lst[i])
    return new

or

def flatten(nested_list):
    flattened_list = []
    for sub_list in nested_list:
        flattened_list.extend(sub_list)
    return flattened_list

Question 19

Writing fibonacci serie for 20 element.

[0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584, 4181, 6765, 10946]

Answer 19

[0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584, 4181, 6765, 10946]

fib = [0,1]

for i in range(20):
fib.append(fib[-1] + fib[-2])

print(fib)

Question 20

def accum(s):
 # your code here

print(accum(‘abcd’))
print(accum(“ZpglnRxqenU”))#, “Z-Pp-Ggg-Llll-Nnnnn-Rrrrrr-Xxxxxxx-Qqqqqqqq-Eeeeeeeee-Nnnnnnnnnn-Uuuuuuuuuuu”))

Answer 20

def accum(s):
  return [x.upper() + x * i for i,x in enumerate(s)] 

print(accum(‘abcd’))
print(accum(“ZpglnRxqenU”))#, “Z-Pp-Ggg-Llll-Nnnnn-Rrrrrr-Xxxxxxx-Qqqqqqqq-Eeeeeeeee-Nnnnnnnnnn-Uuuuuuuuuuu”))

Question 21

return square of each digit as integer

print(square_digits(9119))#, 811181)

Answer 21

print(square_digits(9119))#, 811181)

def square_digits(num):
  string = ''
  for x in str(num):
    string += str(int(x) ** 2)
  return string

#return ““.join([str(i) for i in [int(char) ** 2 for char in str(num)]])

Question 22

print(Descending_Order(0))#, 0)
print(Descending_Order(15736))#, 51)
print(Descending_Order(123456789))#, 987654321)

Answer 22

print(Descending_Order(0))#, 0)
print(Descending_Order(15736))#, 51)
print(Descending_Order(123456789))#, 987654321)

def Descending_Order(num):
  return int("".join(list(reversed(sorted([ x for x in str(num)])))))

or
return int("".join(sorted(list(str(num)), reverse=True)))

Question 23

check the number of x and o’s are equal or not

print(xo(‘xo’)) –> true
print(xo(‘xoOM’)) –> false
print(not xo(‘xxxoo’)) –> true

Answer 23

print(xo(‘xo’)) –> true
print(xo(‘xoOM’)) –> false
print(not xo(‘xxxoo’)) –> true

import re
def xo(s):
  return len(re.findall('[oO]', s)) == len(re.findall('[xX]', s))

without regex –>
s = s.lower()
return s.count(‘o’) == s.count(‘x’)

Question 24

for a = 1 … z = 26

print(words_to_marks(‘attitude’))#, 100)
print(words_to_marks(‘friends’))#, 75)

Answer 24

print(words_to_marks(‘attitude’))#, 100)
print(words_to_marks(‘friends’))#, 75)

def words_to_marks(s):
  res = 0
  lst = [chr(i) for i in range(ord('a'), ord('z')+1)]
  for x in range(len(s)):
    res += lst.index(s[x]) + 1
  return res

alternative solutions –>

return sum(‘_abcdefghijklmnoqprstuvyz’.index(e) for e in s)

return sum(ord(c)-96 for c in s)

Question 25

remove the wovels and count the max of sum of index of letters upto any wovel. print(solve("zodiac"))#,26) print(solve("cautchphrase"))#,73)

Answer 25

print(solve("zodiac"))#,26) print(solve("cautchphrase"))#,73) ``` def solve(s): lst = list(s) num = list('_abcdefghijklmnopqrstuvwxyz') count = 0 arr = [] for x in lst: for first in "aeiou": if x == first: lst[lst.index(x)] = '' arr.append(count) count = 0 if x.lower() not in "aeoui": count += num.index(x) ``` return max(arr)

Question 26

remove the wowels print(solve("zodiac")) --> ['z', 'd', 'c'] print(solve("chruschtschov")) --> ['chr', 'schtsch', 'v']

Answer 26

print(solve("zodiac")) --> ['z', 'd', 'c'] print(solve("chruschtschov")) --> ['chr', 'schtsch', 'v'] ``` import re def solve(s): return re.split('[aeoui]+', s) ```

Question 27

print(persistence(39))#, 3) 3*9 = 27 --> 2*7 = 14 --> 1*4 = 4 --> 3 times print(persistence(4))#, 0) print(persistence(25))#, 2)

Answer 27

print(persistence(39))#, 3) print(persistence(4))#, 0) print(persistence(25))#, 2) import numpy as np ``` def persistence(num): arr = [int(x) for x in str(num)] count = 0 while len(arr) > 1: data = np.multiply.reduce(arr) arr = [int(x) for x in str(data)] count += 1 return count ```

Question 28

check the number is Prime? print(is_prime(0))#, False, '0 is not prime') print(is_prime(1))#, False, '1 is not prime') print(is_prime(17))#, True, '17 is prime')

Answer 28

print(is_prime(0))#, False, '0 is not prime') print(is_prime(1))#, False, '1 is not prime') print(is_prime(17))#, True, '17 is prime') ``` def is_prime(num) if num < 2: return False for i in range(2,num): if num % i == 0: return False return True ```

Question 29

print(alphabet_position("The sunset sets at twelve o' clock."))#, "20 8 5 19 21 14 19 5 20 19 5 20 19 1 20 20 23 5 12 22 5 15 3 12 15 3 11"))

Answer 29

``` def alphabet_position(text): lst = [] for c in text.lower(): if c.isalpha(): lst.append(ord(c)-96) ``` return lst or shortly return [str(ord(c)-96) for c in text.lower() if c.isalpha()]

Question 30

Programming language popularity, from www.tiobe.com/tiobe-index popularity = [["Language", 2017, 2012, 2007, 2002, 1997, 1992, 1987], ["Java", 1, 2, 1, 1, 15, 0, 0], ["C", 2, 1, 2, 2, 1, 1, 1], ["C++", 3, 3, 3, 3, 2, 2, 5], ["C#", 4, 4, 7, 13, 0, 0, 0], ["Python", 5, 7, 6, 11, 27, 0, 0], ["Visual Basic .NET", 6, 17, 0, 0, 0, 0, 0], ["PHP", 7, 6, 4, 5, 0, 0, 0], ["JavaScript", 8, 9, 8, 7, 23, 0, 0], ["Perl", 9, 8, 5, 4, 4, 10, 0]]

Answer 30

format_string = "{:<20} {:>4} {:>4} {:>4} {:>4} {:>4} {:>4} {:>4}" ``` # Display langauges table headers = popularity[0] header_row = format_string.format(*headers) print(header_row) print("-" * len(header_row)) ``` for language in popularity[1:]: print(format_string.format(*language)) print("")

Question 31

difference between range() vs xrange? for i in range(0, 20): for i in xrange(0, 20):

Answer 31

range creates a list, so if you do range(1, 10000000) it creates a list in memory with 9999999 elements. xrange is a sequence object that evaluates lazily. in python3, range does the equivalent of python's xrange

Question 32

Pascal's triangle - 5 level

Answer 32

Binary search tree algorithm ``` class Solution(object): def generate(self, num_rows): """ :type numRows: int :rtype: List[List[int]] """ res = [] if num_rows == 0: return res tmp = [] for j in range(num_rows): tmp = [1] + tmp for i in range(1, len(tmp)-1): tmp[i] += tmp[i+1] ``` return tmp sol = Solution() print sol.generate(5) --> [1, 4, 6, 4, 1]

Question 33

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10] For example, if condition checks bool(item%2) should return: [None, 1, None, 3, None, 5, None, 7, None, 9, None]

Answer 33

[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10] --> [None, 1, None, 3, None, 5, None, 7, None, 9, None] new_items = [x if x % 2 else None for x in items]

Question 34

Given an integer n, write a function that returns count of trailing zeroes in n!. Input: n = 20 Output: 4 Factorial of 20 is 2432902008176640000 which has 4 trailing zeroes.

Answer 34

``` def zeros(n): from functools import reduce if n == 0: return 0 fac = [x for x in range(1, n+1)] res = reduce(lambda x, y: x*y, fac) return len(str(res)) - len(str(res).rstrip('0')) ``` ``` # faster def findTrailingZeros(n): ``` ``` # Initialize result count = 0 ``` ``` # Keep dividing n by # powers of 5 and # update Count i=5 while (n/i>=1): count += int(n/i) i *= 5 ``` return int(count) ``` # recursive def zeros(n): x = n//5 return x + zeros(x) if x else 0 ``` print(zeros(0))#, 0, "Testing with n = 0") print(zeros(6))#, 1, "Testing with n = 6") print(zeros(30000))#, 7, "Testing with n = 30")

Question 35

Warrior game!

Answer 35

``` class Warrior: def __init__(self): self.health = 50 self.attack = 5 ``` ``` @property def is_alive(self) -> bool: return self.health >= 0 ``` ``` class Knight(Warrior): def __init__(self): super().__init__() self.attack = 7 ``` def fight(unit_1, unit_2): while unit_1.is_alive and unit_2.is_alive: unit_2.health -= unit_1.attack if unit_2.is_alive: unit_1.health -= unit_2.attack return unit_1.is_alive ``` chuck = Warrior() chucky = Warrior() bruce = Knight() ``` print(fight(chuck, chucky)) # == True print(chuck.is_alive) #== True print(chucky.is_alive) #== False

Question 36

``` isinstance() issubclass() type() __class__ __class__.__name__ ```

Answer 36

isinstance('a', str) --> True isinstance(5.2, (int, float)) --> True issubclass(bool, int) --> True issubclass(str, int) --> False ``` class Car: def __init__(self, name): self.name = name ``` ``` mycar = Car(name="audi") type(mycar) --> (python 3) type(mycar) --> (python 2.7) mycar.__class__ --> mycar.__class__.__name__ --> 'Car' ```

Question 37

a python generator --> yield definition

Answer 37

``` def square1(data): arr = [] for i in data: arr.append(i*i) return arr ``` ``` def square2(data): for i in data: yield i*i ``` ``` data = [1,2,3,4,5] nums = square2(data) == [x*x for x in data] ``` print square1(data) --> [1, 4, 9, 16, 25] ``` print next(nums) --> 1 print next(nums) --> 4 print next(nums) --> 9 print next(nums) --> 16 print next(nums) --> 25 ``` ``` for num in nums: print num --> 1 4 9 16 25 ```

Question 38

find max x, y with lambda function

Answer 38

find max x, y ``` def max(x,y): if x > y: return x else: return y ``` max = lambda x,y: x if x>y else y print max(8, 5) --> 8

Question 39

use map to calculate the square of items in a list n = [1, 2, 3, 4, 5] print square(n) --> [1, 4, 9, 16, 25]

Answer 39

n = [1, 2, 3, 4, 5] ``` def square(arr): return [x*x for x in arr] ``` print square(n)# --> [1, 4, 9, 16, 25] map(function(x), list) ``` print list(map(lambda x: x*x, n))# --> [1, 4, 9, 16, 25] print list(map(square, n))# --> [1, 4, 9, 16, 25] ```

Question 40

calculate the multiplication of the elements n = [1, 2, 3, 4, 5] --> 120

Answer 40

reduce(function(x,y), list) from functools import reduce n = [1, 2, 3, 4, 5] print reduce(lambda x,y: x*y, n)# --> 120 ``` def mult(n): prod = n[0] for i in range(1,len(n)): prod = prod * n[i] return prod ``` print mult(n)# --> 120

Question 41

reverse a string

Answer 41

reverse a string name = 'hello' print name[::-1] --> 'olleh'

Question 42

class @property and setter method application

Answer 42

class Circle(): ``` def __init__(self, diameter): self.diameter = diameter ``` ``` @property def radius(self): return self.diameter / 2 ``` ``` @radius.setter def radius(self, radius): self.diameter = radius * 2 ``` ``` circ = Circle(20) print(circ.diameter) --> 20 # print circ.radius circ.radius = 30 print(circ.diameter) --> 60 ```

Question 43

Python isbetween two numbers check?

Answer 43

if 1000 <= number <= 3000: pass if not number in range( 1000, 3001): pass

Question 44

print anagrams('abba', ['aabb', 'abcd', 'bbaa', 'dada'])#, ['aabb', 'bbaa']) print anagrams('racer', ['crazer', 'carer', 'racar', 'caers', 'racer'])#, ['carer', 'racer'])

Answer 44

print anagrams('abba', ['aabb', 'abcd', 'bbaa', 'dada'])#, ['aabb', 'bbaa']) print anagrams('racer', ['crazer', 'carer', 'racar', 'caers', 'racer'])#, ['carer', 'racer']) ``` def anagrams(word, words): final = [] sorted_word = ''.join(sorted(word)) for wo in words: if ''.join(sorted(wo)) == sorted_word: final.append(wo) return final ``` ``` def anagrams(word, words): return [item for item in words if sorted(item) == sorted(word)] ``` ``` def anagrams(word, words): return filter(lambda x: sorted(word) == sorted(x), words) ```

Question 45

form will be a matrix like [[A1, A2, A3, ..], [B1, B2, B3, ..]] until AA, AB,...ZY, ZZ to be called with class directly ``` print SpreadSheetHelper()..convert_to_display((2, 1))#, "C2") print SpreadSheetHelper()..convert_to_internal("C2")#, (2, 1)) print SpreadSheetHelper().convert_to_display((0,0))#, (2, 1)) ```

Answer 45

form will be a matrix like [[A1, A2, A3, ..], [B1, B2, B3, ..]] until AA, AB,...ZY, ZZ ``` print SpreadSheetHelper()..convert_to_display((2, 1))#, "C2") print SpreadSheetHelper()..convert_to_internal("C2")#, (2, 1)) ``` import string ``` class SpreadSheetHelper(object): arr = [] ``` @classmethod def convert_to_display(cls, internal): """ Converts an internal coordinate into a display coordinate internal is in the form (row, column) returns a string in the form "CR" where C is the column display name, and R is the row display name """ # form will be a matrix like [[A1, A2, A3, ..], [B1, B2, B3, ..]] alp = string.ascii_uppercase[:] ar2 = [] for l in alp: for idx, val in enumerate(alp): ar2.append(l + val) final = list(alp) + ar2 nums = [str(i) for i in list(range(1,len(final)+1))] for a in final: cls.arr.append([a + x for x in nums]) return cls.arr[internal[0]][internal[1]] # return list(alp).zip(list(len(alp))) # return "A1" @classmethod def convert_to_internal(cls, display): """ Converts a display coordinate into an internal coordinate internal is in the form string "CR" where C is the column display name, and R is the row display name returns a tuple in the form (row, column) """ for idx, set in enumerate(cls.arr): for i, letnum in enumerate(set): if letnum == display: return (idx, i)

Question 46

Python tricks if not -- for strings regex usage set multiple variables by splitting a string

Answer 46

if not -- for strings (means if empty) result = ["", ""] if not result[0]: print False --> False regex usage cell = 'Z9' pat = re.compile(r"^([A-Z]+)([1-9]\d*)$") print pat.match(cell).groups() --> ('Z', '9') set multiple variables by splitting a string cell = 'Z9' col, row = cell print col, row --> Z 9

Question 47

if __name__ == '__main__':

Answer 47

if __name__ == '__main__': when you run a.py from command line it starts from the first line reading the code. If this .py file are imported by other .py files, the code under "the if statement" will not be executed. If this .py are run by python this_py.py under shell, or double clicked in Windows. the code under "the if statement" will be executed. ``` It is usually written for testing. print __name__ --> __main__ when called as a module from another .py file, it writes the name of the file called. ```

Question 48

Closest numbers sorting algo print(closest([1, 3, 5, 12, 56, 76])) --> [1,3,3,5] print(closest([-20, -3916237, -357920, -3620601, 7374819, -7330761, 30, 6246457, -6461594, 266854])) --> [-20, 30]

Answer 48

print(closest([1, 3, 5, 12, 56, 76])) --> [1,3,3,5] print(closest([-20, -3916237, -357920, -3620601, 7374819, -7330761, 30, 6246457, -6461594, 266854])) --> [-20, 30] ``` def closest(arr): s = sorted(arr) new = [] result = [] pairs = list(zip(s, s[1:])) for i in pairs: new.append(abs(i[1] - i[0])) count_arr = [x for x in new if x == min(new)] for c in count_arr: idx = new.index(c) new[idx] = 0 result.append(pairs[idx]) ``` new_list = [] for el in result: new_list.extend([*el]) return new_list

Question 49

The idea behind big O notation?

Answer 49

Big O notation is the language we use for talking about how long an algorithm takes to run. With Big O notation, we use the size of the input, which we call "nn." So we can say things like the runtime grows "on the order of the size of the input" O(n) or "on the order of the square of the size of the input" O(n^2)

Question 50

brute force algorithm

Answer 50

A brute force algorithm finds a solution by trying all possible answers and picking the best one. Say you're a cashier and need to give someone 67 cents (US) using as few coins as possible. How would you do it? You could try running through all potential coin combinations and pick the one that adds to 67 cents using the fewest coins. That's a brute force algorithm, since you're trying all possible ways to make change. Brute force solutions are usually very slow since they involve testing a huge number of possible answers.

Question 51

Python list reverse iteration

Answer 51

Python list reverse iteration arr = [3, 6, 8, 9] for i in range(len(arr), 0, -1): print(arr[i-1]) --> 9 8 6 3 for i in arr[::-1]: print(i) --> 9 8 6 3

Question 52

print(nextnum([9,9,8,7,9]))# --> [9, 9, 8, 8, 0] | print(nextnum([1, 9, 9, 9]))# --> [2, 0, 0, 0]

Answer 52

print(nextnum([9,9,8,7,9]))# --> [9, 9, 8, 8, 0] print(nextnum([1, 9, 9, 9]))# --> [2, 0, 0, 0] ``` def nextnum(arr): carry = 1 result = [] for i in arr[::-1]: sum = i + carry result.append(sum%10) carry = sum//10 if carry: result.append(1) ``` return result[::-1]

Question 53

find first n fibonacci numbers print(fibs(10)) --> [1, 1, 2, 3, 5, 8, 13, 21, 34, 55]

Answer 53

print(fibs) --> [1, 1, 2, 3, 5, 8, 13, 21, 34, 55] ``` a,b = 1,1 fibs = [] for i in range(0,10): fibs.append(a) a, b = b, a+b ``` ``` recursive def fibs(n): if n == 0: return 0 elif n == 1: return 1 else: return fibs(n-2) + fibs(n-1) ```

Question 54

using timeit for a method definition

Answer 54

import timeit ``` setup = ''' def fib(n): a,b = 1,1 for i in range(n-1): a,b = b, a+b return a ''' ``` print min(timeit.Timer('fib(10)', setup=setup).repeat(7, 1000))

Question 55

timeit direct in py file

Answer 55

import timeit ``` def fibs(n): if n == 0: return 0 elif n == 1: return 1 else: return fibs(n-2) + fibs(n-1) ``` print fibs(10) if __name__ == '__main__': import timeit t1 = timeit.Timer("fibs(5)", "from __main__ import fibs") print ("it ran:", t1.timeit(number=1000), "miliseconds")

Question 56

method assertion for testing?

Answer 56

``` def fac(n): assert n>=0, "n asla negatif bir sayi olamaz" if n == 1: return 1 else: return fac(n-1) * n ``` print fac(-5) --> AssertionError: n asla negatif bir sayi olamaz

Question 57

create an array consisting of 0's and 1's randomly

Answer 57

create an array consisting of 0's and 1's randomly import numpy as np arr = np.hstack((np.ones(5),np.zeros(6))) np.random.shuffle(arr) print arr # [ 0. 0. 0. 1. 0. 1. 0. 0. 1. 1. 1.] ``` # alternative a = np.ones(5+7) a[:7] = 0 np.random.shuffle(a) print a # [ 0. 0. 0. 1. 0. 0. 1. 1. 1. 0. 1. 0.] ``` ``` # pythonic ar = np.array([0]*5 + [1]*7) np.random.shuffle(ar) print ar # [0 1 1 1 0 0 1 1 0 1 0 1] ```

Question 58

Timeit with using partial and scatter a plot

Answer 58

import timeit from functools import partial ``` fig_size = plt.rcParams['figure.figsize'] fig_size[0] = 12 fig_size[1] = 12 plt.rcParams['figure.figsize'] = fig_size ``` ``` def maxi(arr): maxi = [] for i in range(len(arr)): for j in range(1,len(arr)): maxi.append(arr[i]*arr[j]) return maxi ``` if __name__=='__main__': complexity = [] size = [] for i in range(2,10): arr = [n for n in np.random.rand(i)] n = arr[-1] t1 = timeit.Timer(partial(maxi, arr)) timespent = t1.timeit(number=1000) complexity.append(timespent) size.append(i) print ("it ran:", timespent, "miliseconds") plt. scatter(size, complexity, color='black', marker='^') plt. show()

Question 59

Lowercase Alphabet in Python

Answer 59

A = string.ascii_lowercase[:] print A --> 'abcdefghijklmnopqrstuvwxyz'

Question 60

use of *, also in def as argument like *args, **kwargs

Answer 60

use of *, also in def as argument like *args, **kwargs ``` def foo(bar, lee): print bar, lee ``` arr = [1, 2] foo(*arr) --> 1 2 ``` def new(*args): for i in args: print i ``` new(1,2,3) - -> 1 - -> 2 - -> 3 ``` def new2(**kwargs): for i in kwargs: print i, kwargs[i] ``` new2(name='one', age=27) - -> age 27 - -> name one

Question 61

Python string manipulation sentence = "To be or not to be"

Answer 61

sentence = "To be or not to be" splitted = sentence.split(" ") set(splitted) --> ["To", "be", "or", "not", "to"] (find the unique words in text) x.istitle() --> if first letter is capital x.startswith('s') x.endswith('s') text.isupper() text.islower() text.capitalize() text.swapcase() text.isalpha() -- check for alphanumeric (cons. of alphabet onyl) text.isdigit() -- consisting of number as strings? text.isalnum() -- consisting of numbers and alphabet text.strip(), text.lstrip(), text.rstrip() --> clean text text.find(s) -- find a substring --> gives the index text.rfind(s) -- reverse find (count from right side) text.replace(u, t) t = 'ozzy' --> list(t) --> ['o', 'z', 'z', 'y']

Question 62

Python read a long txt file

Answer 62

Python read a long txt file f = open('UNDR.txt", 'r') f.readlines() --> return first line f.seek(0) --> reset reading position text = f.read() --> store whole txt in text variable f.read(n) --> read n characters text.splitlines() --> split all lines in a list f.write() --> if opened in 'w' mode