No.161 - leetCode1292

class Solution {
public:
    int maxSideLength(vector<vector<int>>& mat, int threshold) {
        int N = mat.size();
        int M = mat[0].size();
        vector<vector<int>> dp(N+1,vector<int>(M,0));
        for(int i=1;i<=N;i++){
            for(int j=0;j<M;j++){
                dp[i][j] = dp[i-1][j] + mat[i-1][j];
            }
        }
        int ans = 0;
        // 枚举边长
        for(int k=1;k<=min(M,N);k++){
            // 枚举x
            bool flag = true;
            for(int i=k;i<=N && flag;i++){
                long long sum = 0;
                // 枚举y
                for(int j=0;j<k;j++) sum += dp[i][j] - dp[i-k][j];
                if(sum <= threshold) flag = false;
                for(int j=k;j<M && flag;j++){
                    sum += dp[i][j] - dp[i-k][j] - (dp[i][j-k] - dp[i-k][j-k]);
                    if(sum <= threshold) flag = false;
                }
            }
            if(!flag) ans = max(ans,k);
        }
        return ans;
    }
};