矩阵归零

Problem Description

There is a matrix with m rows and n columns. An element of the matrix has at most four adjacent elments(up, down,left,right). You can add a same number to a pair of adjacent elements of the matrix. By doing this operation repeation repeatly, can you make the matrix zero?

Input

A line contains m and n indicating the rows and columns of the matrix. (0<m,n<5)
Each of the following m lines contains n integers(-10^6<=each integer<=10^6)
Input is terminated by one line contains two zeros.

Output

if the matrix can be converted into zero, ouput"Yes" on a line otherwise output "No" on a line.

Sample Input

2 2
1 1
1 0
2 2
0 0
1 1
0 0

Sample Output

No
Yes

# include<cstdio>
# include<iostream>
# include<cstring>
using namespace std;

int a[20][20],n,m;

int main()
{
    //freopen("a.txt","r",stdin);
    while(cin>>m>>n&&n&&m)
    {
        int i,j;
        memset(a,0,sizeof(a));
        for(i=1;i<=m;i++)
            for(j=1;j<=n;j++)
            cin>>a[i][j];
        for(i=1;i<=m;i++)
        {
            if(i%2!=0)
            {
                a[i][1]-=a[i-1][j];
                for(j=2;j<=n;j++)    a[i][j]-=a[i][j-1];
            }
            else
            {
                a[i][n]-=a[i-1][n];
                for(j=n;j>=2;j--)    a[i][j-1]-=a[i][j];
            }
        }
        if((m%2&&a[m][n]==0)||(m%2==0&&a[m][1]==0))
        {
            cout<<"Yes"<<endl;
            continue;
        }
        else    cout<<"No"<<endl;
    }
    return 0;
}