Today I have done leetcode's June LeetCoding Challenge with cpp.

June LeetCoding Challenge 24

Description

Minimum Number of K Consecutive Bit Flips

You are given a binary array nums and an integer k.

A k-bit flip is choosing a subarray of length k from nums and simultaneously changing every 0 in the subarray to 1, and every 1 in the subarray to 0.

Return the minimum number of k-bit flips required so that there is no 0 in the array. If it is not possible, return -1.

A subarray is a contiguous part of an array.

Example 1:

Input: nums = [0,1,0], k = 1
Output: 2
Explanation: Flip nums[0], then flip nums[2].

Example 2:

Input: nums = [1,1,0], k = 2
Output: -1
Explanation: No matter how we flip subarrays of size 2, we cannot make the array become [1,1,1].

Example 3:

Input: nums = [0,0,0,1,0,1,1,0], k = 3
Output: 3
Explanation: 
Flip nums[0],nums[1],nums[2]: nums becomes [1,1,1,1,0,1,1,0]
Flip nums[4],nums[5],nums[6]: nums becomes [1,1,1,1,1,0,0,0]
Flip nums[5],nums[6],nums[7]: nums becomes [1,1,1,1,1,1,1,1]

Constraints:

• 1 <= nums.length <= 105
• 1 <= k <= nums.length

Solution

class Solution {
public:
  int minKBitFlips(vector<int>& nums, int k) {
    int answer = 0;
    int flips = 0;
    for(int i = 0; i < nums.size(); ++i) {
      if(!((nums[i] + flips) % 2)) {
        if(i > nums.size() - k) return -1;
        answer += 1;
        flips += 1;
        nums[i] = - 1;
      }
      if(i + 1 >= k) {
        flips -= (nums[i - k + 1] < 0);
      }
    }
    return answer;
  }
};