URAL 1146 Maximum Sum 最大子矩阵和

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 #include <bits/stdc++.h>
 using namespace std;
 typedef unsigned long long ll;
 const int INF = 0x3f3f3f3f;
 const int M = 2e2+;

 int n;
 int a[M][M];    // a[i][j] 表示从[i][0]到[i][j]的和
 int main()  {
     while( ~scanf("%d", &n ) )  {
         memset( a, , sizeof(a) );
         for( int i=; i<=n; i++ )   {
             for( int j=; j<=n; j++ )   {
                 scanf("%d", &a[i][j] );
                 a[i][j] += a[i][j-];
             }
         }
         int ret = -INF;
         for( int i=; i<=n; i++ )   {
             for( int j=; j<i; j++ )    {
                 int sum = ;
                 for( int h=; h<=n; h++ )   {
                     sum += a[h][i] - a[h][j];
                     ret = max( ret, sum );
                     if( sum <  ) sum = ;
                 }
             }
         }
         printf("%d\n", ret );
     }
     return ;
 }