poj 3278 Catch That Cow（bfs）

题目分析：很水的 BFS ，注意边界

#include<iostream>
#include<cstdio>
#include<memory.h>
#include<queue>
using namespace std;

const int maxn=2100000;
int a[maxn],f[maxn];
int main()
{
	int n,k;
	while(scanf("%d %d",&n,&k)!=EOF)
	{
		int i,j,cur,temp;
		memset(a,0,sizeof(a));
		queue<int>q;
		q.push(n);
		a[n]=1,	f[n]=0;
		while(!q.empty())
		{
			cur=q.front();
			q.pop();
            if(cur==k)
				break;
			temp=cur-1;
			//printf("%d*\t",cur);
			if(temp>=0 && a[temp]==0)
			{
				q.push(temp);
				a[temp]=1;
				f[temp]=f[cur]+1;	
			}
			temp=cur+1;
			if(a[temp]==0 && temp<=k)
			{
				q.push(temp);
				a[temp]=1;
				f[temp]=f[cur]+1;
			}
			temp=cur*2;
			if(a[temp]==0&&temp<=2*k)//注意下是2*k
			{                        //不是k
				q.push(temp); 
				a[temp]=1;
				f[temp]=f[cur]+1;
			}
		}
		printf("%d\n",f[cur]);
	}
	return 0;
}