POJ 3278 bfs

传送门：http://poj.org/status

还以为会超时。。。

bfs代码：

#include <iostream>
#include <queue>
#include <cstdio>
#include <cstring>
using namespace std;

struct p
{
	int i; //位置
	int j; //步数
};
queue <struct p> q;
int n , k;
int v;
const int maxn = 200000;
int vis[maxn];

void bfs(int i)
{
	struct p now;
	now.i = i;
	now.j = 0;
	q.push(now);
	vis[now.i] = 1;
	while(!q.empty())
	{
		now = q.front();
		q.pop();
		if(now.i == k)
		{
			if(now.j < v || v == -1) v = now.j;
		}
		else
		{
			struct p now1;
			now1 = now;
			if(now.i + 1 >= 0 && now.i + 1 <= maxn && !vis[now.i + 1])
			{
				now1.i ++;
				now1.j ++;
				q.push(now1);
				vis[now1.i] = 1;
			}
			now1 = now;
			if(now.i - 1 >= 0 && now.i - 1 <= maxn && !vis[now.i - 1])
			{
				now1.i --;
				now1.j ++;
				q.push(now1);
				vis[now1.i] = 1;
			}
			now1 = now;
			if(2 * now.i>= 0 && 2 * now.i <= maxn && !vis[now.i * 2])
			{
				now1.i *= 2;
				now1.j ++;
				q.push(now1);
				vis[now1.i] = 1;
			}
		}
	}
}


int main()
{
	scanf("%d%d",&n, &k);
	v = -1;
	memset(vis,0,sizeof(vis));
	bfs(n);
	printf("%d",v);
}