WarmUp-2.py

#Given a string and a non-negative int n, return a larger string that is n copies of the original string.
def string_times(str, n):
  return str*n

#Given a string and a non-negative int n, we'll say that the front of the string is the first 3 chars, or whatever is there if the string is less than length 3. Return n copies of the front;
def front_times(str, n):
  if(len(str)<=3):
    return str*n
  else:
    return str[0:3]*n

#Given a string, return a new string made of every other char starting with the first, so "Hello" yields "Hlo".
def string_bits(str):
  return str[::2]

#Given a non-empty string like "Code" return a string like "CCoCodCode".
def string_splosion(str):
  result = ""
  # On each iteration, add the substring of the chars 0..i
  for i in range(len(str)):
    result = result + str[:i+1]
  return result

#Given a string, return the count of the number of times that
#  a substring length 2 appears in the string and also as the
# last 2 chars of the string, so "
# hixxxhi" yields 1 (we won't count the end substring).
def last2(str):
    # Screen out too-short string case.
    if len(str) < 2:
        return 0

    # last 2 chars, can be written as str[-2:]
    last2 = str[len(str) - 2:]
    count = 0

    # Check each substring length 2 starting at i
    for i in range(len(str) - 2):
        sub = str[i:i + 2]
        if sub == last2:
            count = count + 1

    return count

#Given an array of ints, return the number of 9's in the array.
def array_count9(nums):
  return nums.count(9)

#Given an array of ints, return True if one of the first 4 elements in the array is a 9. The array length may be less than 4.
def array_front9(nums):
  if(len(nums)<=4):
    return 9 in nums
  else:
    return 9 in nums[:4]

#Given an array of ints, return True if the sequence of numbers 1, 2, 3 appears in the array somewhere.
def array123(nums):
    l = [1, 2, 3]
    for x in nums:
        if (x in l):
            l.remove(x)
    return len(l) == 0

"""
Given 2 strings, a and b, return the number of the positions where they contain the same length 2 substring. So "xxcaazz" and "xxbaaz" yields 3, since the "xx", "aa", and "az" substrings appear in the same place in both strings.

string_match('xxcaazz', 'xxbaaz') → 3
string_match('abc', 'abc') → 2
string_match('abc', 'axc') → 0
"""
def string_match(a, b):
    # Figure which string is shorter.
    shorter = min(len(a), len(b))
    count = 0

    # Loop i over every substring starting spot.
    # Use length-1 here, so can use char str[i+1] in the loop
    for i in range(shorter - 1):
        a_sub = a[i:i + 2]
        b_sub = b[i:i + 2]
        if a_sub == b_sub:
            count = count + 1

    return count