最大子矩陣和（n^2*m,dp，前綴和)

INPUT：
5 4
-1 -2 -3 -4
-3 -2 2 4
-3 -4 3 5
4 -5 3 6
-3 -2 -1 0
OUTPUT
23

前綴和+dp優化

#include<iostream>
using namespace std;
const int maxn=600;

int n,m;

long long f[maxn];
long long s[maxn][maxn];

int main(){
    cin>>n>>m;
    for (int i=1;i<=n;i++){
        s[i][0]=0;
        int data;
        for (int j=1;j<=m;j++){
            cin>>data;
            s[i][j]=s[i-1][j]+s[i][j-1]-s[i-1][j-1]+data;
    }
    }   
    long long  ans=-(1<<30); 
    for (int x1=1;x1<=n;x1++)
        for (int x2=x1;x2<=n;x2++){
            for (int y=1;y<=m;y++) {
                long long sum=s[x2][y]-s[x1-1][y]-s[x2][y-1]+s[x1-1][y-1];
                if (f[y-1]<0) f[y]=sum;
                else f[y]=f[y-1]+sum;
                if (f[y]>ans) ans=f[y];     //壓縮
    }
}
    cout<<ans;
}