蒟蒻求助

前缀和dp

我也知道这么短的代码肯定不对

16分WA，但重点是我硬是没hACk掉

#include <iostream>
#include <cstdio>
using namespace std;
int dp[2505][2505], leftpre[2505][2505], rightpre[2505][2505], ans;
bool fish[2505][2505];
int main() {
    int n, m;
    cin >> n >> m;
    for(int i = 1; i <= n; i++) 
        for(int j = 1; j <= m; j++) {
            int x;
            scanf("%d", &x);
            fish[i][j] = x;
        }
    for(int i = 1; i <= n; i++) 
        for(int j = 1; j <= m; j++) 
            if(fish[i][j]) {
                leftpre[i][j] = leftpre[i - 1][j - 1] + 1;
                rightpre[i][j] = rightpre[i + 1][j + 1] + 1;
            }
    for(int i = 1; i <= n; i++) {
        for(int j = 1; j <= m; j++) {
            if(fish[i][j]) dp[i][j] = max(leftpre[i][j], rightpre[i][j]);
            ans = max(dp[i][j], ans);
        }
    }
    cout << ans;
    return 0;
}