Given an N*N matrix, find the coolest square sub-matrix.
We define the cool value of the square matrix as X-Y where X indicating the sum of all integers of the main diagonal and Y indicating the sum of the other diagonal.

The first line has a positive integer N (2 ≤ N ≤ 400), the size of the matrix.
The following N lines each contain N integers in the range [-1000, 1000], the elements of the matrix.

Output the coolest value of a square sub-matrix.

#include<bits/stdc++.h>

#define MAX 405

using namespace std;

int A1[MAX][MAX],A2[MAX][MAX];//A1正对角线前缀和 与 A2反对角线前缀和

int main()

{

    int i,j,k,n,x,maxx=-;

    cin>>n;

    for(i=;i<=n;i++)

    {

        for(j=;j<=n;j++)

        {

            scanf("%d",&x);

            A1[i][j]=A1[i-][j-]+x;//左上加到右下

            A2[i][j]=A2[i-][j+]+x;//右上加到左下

        }

    }

    for(i=;i<=n;i++)    //起始行位置i

        for(j=;j<=n;j++)//起始列位置j

            for(k=;k<=min(n+-i,n+-j);k++)//小矩阵边长k

                maxx=max(maxx,A1[i+k][j+k]-A1[i-][j-]-(A2[i+k][j]-A2[i-][j+k+]));

    cout<<maxx<<endl;

    return ;

}