bfs sample problem

#include<vector>
#include<stdio.h>
#include<iostream>
#include<queue>

using namespace std;

char grid[1010][1010];
int vis[1010][1010];
int n,m;
int dx[4]={0,0,1,-1};
int dy[4]={-1,1,0,0};

void bfs(int srcx,int srcy)
{
    int i,vx,vy,ux,uy;
    vis[srcx][srcy]=1;

    queue< pair<int,int> > Q;
    Q.push( make_pair(srcx,srcy) );
    while(!Q.empty())
    {
        ux=Q.front().first;
        uy=Q.front().second;
        Q.pop();

        for(int k=0;k<4;k++)
        {
            vx=ux+dx[k];
            vy=uy+dy[k];
            if(vx>=0 && vx<n && vy>=0 && vy<m && vis[vx][vy]==0)
            {
                vis[vx][vy]=vis[ux][uy]+1;
                Q.push(make_pair(vx,vy));
            }
        }
    }
}


int main()
{


    freopen("in.txt","r",stdin);
    int i,j,k,i2,j2;
    cin>>n;
    n=2*n-1;
    m=n;
    bfs(n/2,n/2);


    for(i=0;i<n;i++)
    {
        for(j=0;j<m;j++)
        {
            cout<<vis[i][j];
        }
        cout<<endl;
    }

    return 0;
}
///dfs http://pastebin.com/T0GyaHQX
///shortest path using dfs http://pastebin.com/HEtHBfrR
///bfs http://pastebin.com/bAaeTuCm