bzoj 1646: [Usaco2007 Open]Catch That Cow 抓住那只牛【bfs】

#include<iostream>
#include<cstdio>
#include<queue>
using namespace std;
const int N=200005;
int s,t,d[N];
bool v[N];
queue<int>q;
inline void wk(int x,int y)
{
    d[y]=d[x]+1;
    if(!v[y])
    {
        v[y]=1;
        q.push(y);
    }
}
int main()
{
    scanf("%d%d",&s,&t);
    for(int i=0;i<=200000;i++)
        d[i]=1e9;
    v[s]=1,d[s]=0,q.push(s);
    while(!q.empty())
    {
        int u=q.front();
        q.pop();
        v[u]=0;
        if(u*2<=200000&&d[u*2]>d[u]+1)
            wk(u,u*2);
        if(u+1<=200000&&d[u+1]>d[u]+1)
            wk(u,u+1);
        if(u-1>=0&&d[u-1]>d[u]+1)
            wk(u,u-1);
    }
    printf("%d\n",d[t]);
    return 0;
}