Program to count number of nice subarrays in Python

Suppose we have an array called nums and another value k. We have to find the number of nice sub-arrays. A subarray is said to be nice subarray if there are k odd numbers on it.

So, if the input is like nums = [1,1,2,1,1], k = 3, then the output will be 2 because there are two subarrays [1,1,2,1] and [1,2,1,1].

To solve this, we will follow these steps −

• odd_i := a new list

• for i in range 0 to size of nums - 1, do

  • if nums[i] mod 2 is same as 1, then

    • insert i at the end of odd_i

• start := 0, end := k - 1

• i := 0

• count := 0

• while end < size of odd_i, do

  • if end is same as size of odd_i - 1, then

    • j := size of nums - 1

  • otherwise,

    • j := odd_i[end + 1] - 1

  • count := count +(odd_i[start] - i + 1) *(j - odd_i[end] + 1)

  • i := odd_i[start] + 1

  • start := start + 1

  • end := end + 1

• return count

Example

Let us see the following implementation to get better understanding −

def solve(nums, k):
   odd_i = []
   for i in range(len(nums)):
      if nums[i] % 2 == 1:
         odd_i.append(i)
   start = 0
   end = k - 1
   i = 0
   count = 0
   while end < len(odd_i):
      if end == len(odd_i) - 1:
         j = len(nums) - 1
      else:
         j = odd_i[end + 1] - 1
      count = count + (odd_i[start] - i + 1) * (j - odd_i[end] + 1)
      i = odd_i[start] + 1
      start = start + 1
      end = end + 1
   return count

nums = [1,1,2,1,1]
k = 3
print(solve(nums, k))

Input

[1,2,3,4,5,6,7,8]

Output

2