king's trouble II

Description
Long time ago, a king occupied a vast territory.
Now there is a problem that he worried that he want to choose a largest square of his territory to build a palace.
Can you help him?
For simplicity, we use a matrix to represent the territory as follows:
0 0 0 0 0
0 1 0 1 0
1 1 1 1 0
0 1 1 0 0
0 0 1 0 0
Every single number in the matrix represents a piece of land, which is a 1*1 square
1 represents that this land has been occupied
0 represents not
Obviously the side-length of the largest square is 2

Input
The first line of the input contains a single integer t (1≤t≤5) — the number of cases.
For each case
The first line has two integers N and M representing the length and width of the matrix
Then M lines follows to describe the matrix
1≤N,M≤1000

Output
For each case output the the side-length of the largest square

Sample Input
2
5 5
0 0 0 0 0
0 1 0 1 0
1 1 0 1 0
0 1 1 0 0
0 0 1 0 0
5 5
0 0 0 0 0
0 1 0 1 0
1 1 1 1 0
0 1 1 0 0
0 0 1 0 0

Sample Output
1
2

dp

#include<stdio.h>#include<iostream>#include<string.h>using namespace std;int a[1010][1010];int dp[1010][1010];int main(){    int t;    scanf("%d",&t);    while(t--)    {        int n,m;        scanf("%d%d",&n,&m);        memset(dp,0,sizeof(dp));        for(int i=0;i<n;i++)        {            for(int j=0;j<m;j++)            {                scanf("%d",&a[i][j]);            }        }        int ans=0;        for(int i=1;i<n;i++)        {            for(int j=1;j<m;j++)            {                if(a[i][j]==1)                {                    dp[i][j]=min(dp[i][j-1],min(dp[i-1][j-1],dp[i-1][j]))+1;                }                 ans=max(ans,dp[i][j]);            }        }        printf("%d\n",ans);    }}