Maximum Ones After Modification

• Time : $O(n)$
• Space : $O(1)$

int Solution::solve(vector<int> &A, int B) {
    int res = 0, l = 0, r = 0, n = A.size(), now = 0;
    while(r < n) {
        while(r < n and now <= B) {
            res = max(res, r - l);
            if(A[r++] == 0) now += 1;
        }
        if(now <= B) res = max(res, r - l);
        while(now > B) {
            if(A[l++] == 0) now -= 1;
        }
    }
    return res;
}