> For the complete documentation index, see [llms.txt](https://jimmylin1991.gitbook.io/practice-of-algorithm-problems/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://jimmylin1991.gitbook.io/practice-of-algorithm-problems/array/1004.-max-consecutive-ones-iii.md).

# 1004. Max Consecutive Ones III

Given an array `A` of 0s and 1s, we may change up to `K` values from 0 to 1.

Return the length of the longest (contiguous) subarray that contains only 1s. 

**Example 1:**

```
Input: A = [1,1,1,0,0,0,1,1,1,1,0], K = 2
Output: 6
Explanation: 
[1,1,1,0,0,1,1,1,1,1,1]
Bolded numbers were flipped from 0 to 1.  The longest subarray is underlined.
```

**Example 2:**

```
Input: A = [0,0,1,1,0,0,1,1,1,0,1,1,0,0,0,1,1,1,1], K = 3
Output: 10
Explanation: 
[0,0,1,1,1,1,1,1,1,1,1,1,0,0,0,1,1,1,1]
Bolded numbers were flipped from 0 to 1.  The longest subarray is underlined.
```

**Note:**

1. `1 <= A.length <= 20000`
2. `0 <= K <= A.length`
3. `A[i]` is `0` or `1`&#x20;

```cpp
// Sliding window
int longestOnes(vector<int>& A, int K) { // time: O(n); space: O(1)
    int res = 0, zero_cnt = 0, begin = 0, end = 0;
    while (end < A.size()) {
        if (A[end++] == 0) ++zero_cnt;
        if (zero_cnt > K && A[begin++] == 0) --zero_cnt;
        res = max(res, end - begin);
    }
    return res;
}
```

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