POJ 3620 Avoid The Lakes

http://poj.org/problem?id=3620

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
int map[105][105];
int vis[105][105];
int max1;
int ans;
int dist[4][2]={-1,0,0,-1,1,0,0,1};
void dfs(int x1,int y1)
{
    for(int i=0;i<4;i++)
    {
        int x,y;
        x=x1+dist[i][0];
        y=y1+dist[i][1]; //cout<<x<<'m'<<y<<endl;
        if(map[x][y]==1&&!vis[x][y])
        {
            vis[x][y]=1;
            dfs(x,y);
            ans++;
        }
    }

}
int main()
{
    int n,m,k,i,j;
    while(scanf("%d%d%d",&n,&m,&k)!=EOF)
    {
        memset(map,0,sizeof(map));
        memset(vis,0,sizeof(vis));
        for(i=0;i<k;i++)
        {
            int a,b;
            scanf("%d%d",&a,&b);
            map[a][b]=1;
        }
        max1=0;
        for(i=1;i<=n;i++)
        {
            for(j=1;j<=m;j++)
            {
               // cout<<i<<' '<<j<<endl;
                if(map[i][j])
                {
                    ans=1;
                    vis[i][j]=1;
                    dfs(i,j);
                    if(ans>max1) max1=ans;
                }
            }

        }
        cout<<max1<<endl;
    }
    return 0;
}