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Program to count minimum k length sublist that can be flipped to make all items of list to 0 in Python

Suppose we have a list of numbers called nums that stored 0s and 1s. We have another value k.

Now consider there is an operation where we flip a sublist of length k such that all 1s will be 0s and all 0s will be 1s. We have to find the minimum number of operations required to change nums into all 1s to 0s. If we cannot change it return -1.

So, if the input is like nums = [1,1,1,0,0,1,1,1], k = 3, then the output will be 2, as we can flip the first three numbers to zero and then flip the last three numbers to zero.

To solve this, we will follow these steps −

  • n := size of nums

  • res := 0, flipped := 0

  • to_conv := a list of size n and fill with 0

  • for i in range 0 to n, do

    • flipped := flipped XOR to_conv[i]

    • cur := nums[i]

    • cur := cur XOR flipped

    • if cur is same as 1, then

      • flipped := flipped XOR 1

      • res := res + 1

      • if i + k - 1 >= n, then

        • return -1

      • if i + k < n, then

        • to_conv[i + k] := 1

  • return res

Example 

Let us see the following implementation to get better understanding −

class Solution:
   def solve(self, nums, k):
      n = len(nums)
      res = 0
      flipped = 0
      to_conv = [0] * n
      for i in range(n):
         flipped ^= to_conv[i]
         cur = nums[i]
         cur ^= flipped
         if cur == 1:
            flipped ^= 1
            res += 1
            if i + k - 1 >= n:
               return -1
            if i + k < n:
               to_conv[i + k] = 1
      return res
ob = Solution()
nums = [1,1,1,0,0,1,1,1]
k = 3
print(ob.solve(nums, k))

Input

[1,1,1,0,0,1,1,1], 3

Output

2