题解 | #最大子矩阵#

#include <iostream>
using namespace std;

int main() {

    int N;
    cin >> N;
    int a[100][100];
    int i;
    int j;
    int b[100][100];
    for(i = 0; i < N; i++) {
        for(j = 0; j < N; j++) {
            cin >> a[i][j];
            if(i == 0 && j == 0) {
                b[i][j] = a[i][j];
            }
            else if(i == 0 && j != 0) {
                b[i][j] = b[i][j - 1] + a[i][j];
            }
            else if(i != 0 && j == 0) {
                b[i][j] = b[i - 1][j] + a[i][j];
            }
            else {
                b[i][j] = b[i][j - 1] + b[i - 1][j] - b[i - 1][j - 1] + a[i][j];
            }
        }
    }

    int maxM = -127;
    int sum = 0;
    for(int x1 = 0; x1 < N ; x1++) {
        for(int y1 = 0; y1 < N; y1++) {
            for(int x2 = x1; x2 < N; x2++) {
                for(int y2 = y1; y2 < N; y2++) {
                    if(x1 == 0 && y1 == 0) {
                        sum = b[x2][y2];
                    }
                    else if(x1 == 0 && y1 != 0) {
                        sum = b[x2][y2] - b[x2][y1 - 1];
                    }
                    else if(x1 != 0 && y1 == 0) {
                        sum = b[x2][y2] - b[x1 - 1][y2];
                    }
                    else {
                        sum = b[x2][y2] - b[x1 - 1][y2] - b[x2][y1 - 1] + b[x1 - 1][y1 - 1];
                    }
                   // cout << "sum = " << sum << endl;
                    maxM = maxM > sum ? maxM : sum;
                }
            }
        }
    }
    cout << maxM << endl;
}
// 64 位输出请用 printf("%lld")