poj 3278 Catch That Cow 广度优先算法

#include <iostream>
#include <queue>
#define SIZE 100001

using namespace std;

queue<int> x;
bool visited[SIZE];
int step[SIZE];

int bfs(int n, int k)
{
	int head, next;
	//起始节点入队
	x.push(n);
	//标记n已访问 
	visited
 = true;
	//起始步数为0 
	step
 = 0; 
	//队列非空时 
	while (!x.empty())
	{
		//取出队头 
		head = x.front();
		//弹出队头 
		x.pop();
		//3个方向搜索 
		for (int i = 0; i < 3; i++)
		{
			if (i == 0) 
				next = head - 1;
			else if (i == 1) 
				next = head + 1;
			else 
				next = head * 2;
			//越界就不考虑了 
			if (next > SIZE || next < 0) 
				continue;
			//判重 
			if (!visited[next])
			{
				//节点入队 
				x.push(next);
				//步数+1 

				step[next] = step[head] + 1;
				//标记节点已访问 
				visited[next] = true;
			}
			//找到退出 
			if (next == k) 
				return step[next];
		}
	}
	return 0;
}

int main()
{
	int n, k;
	cin >> n >> k;
	if (n >= k)
		cout << n - k << endl;
	else
		cout << bfs(n, k) << endl;
	return 0;
}