HDU 1081 To The Max

#include<stdio.h>
#include<string.h>
#include<algorithm>
using namespace std;

const int INF=0x3f3f3f3f;
const int N=110;

int main ()
{
    int n, i, j, k, Max, sum, Map[N][N], num;

    while (scanf("%d", &n) != EOF)
    {
        memset(Map, 0, sizeof(Map));

        for (i = 1; i <= n; i++)
        {
            for (j = 1; j <= n; j++)
            {
                scanf("%d", &num);
                Map[i][j] = Map[i][j-1] + num; ///保存第i行前j列的和
            }
        }

        Max = -INF;

        for (i = 1; i <= n; i++) ///列
        {
            for (j = i; j <= n; j++) ///列 
            {
                sum = 0;

                for (k = 1; k <= n; k++) ///行
                {
                    if (sum < 0) sum = 0; ///sum小于0时加上其它的数会变小，我们要找最大的和，所以重新置为0

                    sum += Map[k][j]-Map[k][i-1]; ///sum记录前k行第i~j列的和

                    if (sum > Max) Max = sum; ///Max保存最大值
                }
            }
        }

        printf("%d\n", Max);
    }

    return 0;
}