POJ 2243 Knight Moves

#include<cstdio>
#include<cstring>
#include<cmath>
#include<queue>
#include<vector>
#include<algorithm>
#include<iostream>
#define INF 0x7fffffff
using namespace std;
struct lx
{
    int x,y;
    int lv;
};
lx start,thend;
int xx[]={-2,-2,-1,-1,1,1,2,2};
int yy[]={1,-1,2,-2,2,-2,1,-1};
bool vis[10][10];
int bfs()
{
    queue<lx>q;
    lx tmp;
    memset(vis,0,sizeof(vis));
    start.lv=0;
    q.push(start);
    vis[start.x][start.y]=1;
    while(!q.empty())
    {
        tmp=q.front();q.pop();
        vis[tmp.x][tmp.y]=1;
        if(tmp.x==thend.x&&tmp.y==thend.y)
        return tmp.lv;
        for(int k=0;k<8;k++)
        {
            int x=tmp.x+xx[k];
            int y=tmp.y+yy[k];
            if(x>8||x<1||y>8||y<1||vis[x][y])continue;
            lx now;
            now.x=x,now.y=y,now.lv=tmp.lv+1;
            q.push(now);
        }
    }
    return -1;
}

int main()
{
    char sa[3],sb[3];
    while(scanf("%s%s",sa,sb)!=EOF)
    {
        start.x=sa[0]-'a'+1;
        start.y=sa[1]-'0';
        thend.x=sb[0]-'a'+1;
        thend.y=sb[1]-'0';
        int tp=bfs();
        printf("To get from %s to %s takes %d knight moves.\n",sa,sb,tp);
    }
    return 0;
}