POJ 1050 二维动态规划转变成枚举加一维的动态规划！

#include <cstdio>
#include <iostream>
#include <algorithm>
#include <queue>
#include <stack>
#include <climits>
#include <cstring>
#include <cmath>
#include <map>
#include <set>

using namespace std;

int n;
int a[105][105];
int dp[105][105];
int sum[105][105];

int main(){
	while(scanf("%d",&n)!=EOF){
		for(int i = 1;i <= n;i++){
			for(int j = 1;j <= n;j++){
				scanf("%d",&a[i][j]);
			}
		}
		memset(dp,0,sizeof(dp));
	
		for(int j = 1;j <= n;j++){ // j列的前缀和 
			for(int i = 1;i <= n;i++){
				sum[j][i] = sum[j][i-1] + a[i][j];
			}
		}
		for(int i = 1;i <= n;i++){
			for(int j = i;j <= n;j++){
				int right = 0;
				for(int k = 1;k <= n;k++){
					 if(right >= 0){
					 	right += sum[k][j] - sum[k][i-1]; 
					 }
					 else{
					 	right = sum[k][j] - sum[k][i-1]; 
					 }
					 
					 dp[i][j] = max(dp[i][j],right);
					 
				} 
			}
		}		
		int ans = -INT_MAX;
		for(int i = 1;i <= n;i++){
			for(int j = i;j <= n;j++){
				if(dp[i][j] > ans){
					ans = dp[i][j];
				}
			}
		}
		cout << ans << endl;
	}
	return 0;
}