Catch That Cow（BFS）

http://poj.org/problem?id=3278

#include<stdio.h>
#include<string.h>
#include<queue>
#define MAX 1000002
using namespace std;
int vis[MAX],step[MAX];
int dir[3][2] = {{1,1},{1,-1},{2,0}};
queue <int> q;
int n,m;
void bfs(int s)
{
    vis[s] = 1;
    q.push(s);
    while(!q.empty())
    {
        s = q.front();
        q.pop();
        for (int i = 0; i < 3; i ++)
        {
            int x = s*dir[i][0] + dir[i][1];
            if(!vis[x] && x >= 0 && x < MAX)
            {
                if(x==m)
                {
                    step[x] = step[s] + 1;
                    return ;
                }
                else
                {
                    q.push(x);
                    vis[x] = 1;
                    step[x] = step[s] + 1;
                }
            }
        }
    }
}
int main()
{
    scanf("%d%d",&n,&m);
    memset(vis,0,sizeof(vis));
    memset(step,0,sizeof(step));
    bfs(n);
    printf("%d\n",step[m]);
    return 0;
}