#1004 - Max Consecutive Ones III

MediumSliding Window

Given a binary array nums and an integer k, return the maximum number of consecutive 1's in the array if you can flip at most k 0's.

Input	Output
nums = [1,1,1,0,0,0,1,1,1,1,0], k = 2	6
nums = [0,0,1,1,0,0,1,1,1,0,1,1,0,0,0,1,1,1,1], k = 3	10

Solution Space

Try it

/**
 * Returns the longest subarray of 1's achievable by flipping at most k 0's.
 *
 * @param nums Binary array (only 0s and 1s)
 * @param k    Maximum number of 0→1 flips allowed
 * @returns    Length of the longest all-1 window after flips
 */
export function longestOnes(nums: number[], k: number): number {
  let left = 0;
  let zeros = 0;
  let max = 0;

  for (let right = 0; right < nums.length; right++) {
    if (nums[right] === 0) zeros++;

    // Shrink window until it contains at most k zeros
    while (zeros > k) {
      if (nums[left] === 0) zeros--;
      left++;
    }

    max = Math.max(max, right - left + 1);
  }

  return max;
}

Approach: variable-size sliding window – expand `right` unconditionally; when the window has more than `k` zeros, advance `left` until the constraint is restored.

Time: O(n) – each element is visited at most twice (once by `right`, once by `left`).

Space: O(1) – only a few integer variables.

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