POJ - 3278 Catch That Cow 简单搜索bfs

题目链接
题目给了奶牛的坐标，终点的坐标；
我们有三种走法x-1，x+1，2*x，求步数；

#include <iostream>
#include <cstdio>
#include <queue>
#include<cstring>
#include<map>
using namespace std;
struct p
{
    int n;
    int l;
};
int change(int i,int x)
{
    if(i==0)return x-1;
    else if(i==1)return x+1;
    else return 2*x;
}
int main()
{
    int n,k;
    scanf("%d%d",&n,&k);
    if(n>k)
    {
        printf("%d\n",n-k);
        return 0;
    }
    if(n==k)
    {
        printf("0\n");
        return 0;
    }
    p now,next;
    now.n=n,now.l=0;
    map<int,bool>a;
    queue<p>q;
    a[n]=1;
    q.push(now);
    while(!q.empty())
    {
        now=q.front();
        for(int i=0; i<3; i++)
        {
            next=now;
            next.n=change(i,now.n);
            if(next.n==k)
            {
                next.l++;
                printf("%d\n",next.l);
                return 0;
            }
            if(next.n>=0&&next.n<=100000&&a[next.n]==0)
            {
                next.l++;
                a[next.n]=1;
                q.push(next);
            }
        }
        q.pop();
    }
    return 0;
}