HDU 1081 To The Max（最大子矩阵）

/*
题意:求子矩阵的最大和

题解：这一类型的题，关键在压缩，将矩阵压缩为一维数组，然后转变为求最大字段和
*/

#include <iostream>
using namespace std;
const int nMax = 107;
const int INF = 0x7fffffff;
//int d[nMax][nMax][nMax];
int N;
int map[nMax][nMax];
int sum[nMax][nMax];
int res[nMax], _ans[nMax];
int _max;
int main()
{
while(scanf("%d", &N) != EOF && N)
{
_max = -INF;
int i, j, k;
for(i = 1; i <= N; ++ i)
{
sum[i][0] = 0;
for(j = 1; j <= N; ++ j)
{
scanf("%d", &map[i][j]);
sum[i][j] = sum[i][j - 1] + map[i][j];
}
}
for(i = 1; i <= N; ++ i)
{
for(j = i; j <= N; ++ j)
{
_ans[0] = 0;
for(k = 1; k <= N; k ++)
{
res[k] = sum[k][j] - sum[k][i - 1];
_ans[k] = _ans[k - 1] + res[k];
}
int min = 0;
for(k = 1; k <= N; k ++)
{
if(_ans[k] - min > _max)
_max = _ans[k] - min;
if(_ans[k] < min)
min = _ans[k];
}
}
}
printf("%d\n", _max);
}
return 0;
}