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CodingBat -> Python -> List-2

count_evens

Return the number of even ints in the given array. Note: the % "mod" operator computes the remainder, e.g. 5 % 2 is 1.

count_evens([2, 1, 2, 3, 4]) → 3
count_evens([2, 2, 0]) → 3
count_evens([1, 3, 5]) → 0

def count_evens(nums):
  count = 0
  for i in range(len(nums)):
    if nums[i] % 2 == 0:
      count += 1
  return count

big_diff

Given an array length 1 or more of ints, return the difference between the largest and smallest values in the array. Note: the built-in min(v1, v2) and max(v1, v2) functions return the smaller or larger of two values.

big_diff([10, 3, 5, 6]) → 7
big_diff([7, 2, 10, 9]) → 8
big_diff([2, 10, 7, 2]) → 8

def big_diff(nums):
  return max(nums) - min(nums)

centered_average

Return the "centered" average of an array of ints, which we'll say is the mean average of the values, except ignoring the largest and smallest values in the array. If there are multiple copies of the smallest value, ignore just one copy, and likewise for the largest value. Use int division to produce the final average. You may assume that the array is length 3 or more.

centered_average([1, 2, 3, 4, 100]) → 3
centered_average([1, 1, 5, 5, 10, 8, 7]) → 5
centered_average([-10, -4, -2, -4, -2, 0]) → -3

def centered_average(nums):
  nums.sort()
  count = 0
  total = 0
  for i in range(1, len(nums) - 1):
    count += 1
    total += nums[i]
  return total / count

sum13

Return the sum of the numbers in the array, returning 0 for an empty array. Except the number 13 is very unlucky, so it does not count and numbers that come immediately after a 13 also do not count.

sum13([1, 2, 2, 1]) → 6
sum13([1, 1]) → 2
sum13([1, 2, 2, 1, 13]) → 6

def sum13(nums):
  total = 0
  skip = False
  if len(nums) == 0:
    return 0
  else:
    for i in range(len(nums)):
      if nums[i] == 13:
        skip = True
      elif skip:
        skip = False
      else:
        total += nums[i]
  return total

sum67

Return the sum of the numbers in the array, except ignore sections of numbers starting with a 6 and extending to the next 7 (every 6 will be followed by at least one 7). Return 0 for no numbers.

sum67([1, 2, 2]) → 5
sum67([1, 2, 2, 6, 99, 99, 7]) → 5
sum67([1, 1, 6, 7, 2]) → 4

def sum67(nums):
  total = 0
  skip = False
  for i in range(len(nums)):
    if nums[i] == 6:
      skip = True
    elif nums[i] == 7 and skip:
      skip = False
    elif not skip:
      total += nums[i]
  return total

has22

Given an array of ints, return True if the array contains a 2 next to a 2 somewhere.

has22([1, 2, 2]) → True
has22([1, 2, 1, 2]) → False
has22([2, 1, 2]) → False

def has22(nums):
  has2 = False
  for i in range(len(nums)):
    if has2 and nums[i] == 2:
      return True
    elif nums[i] == 2:
      has2 = True
    else:
      has2 = False
  return False