POJ3278http://poj.org/problem?id=3278

http://poj.org/problem?id=3278

题目大意： m，n两个数m可+1， -1， *2变成n，需要经过几步

#include<stdio.h>
#include<stdlib.h>
#include<math.h>
#include<string.h>
#include<queue>
#define max(a, b)(a > b ? a : b)
#define N 100010

using namespace std;

struct node
{
    int x, step;
};

int m, n;
bool vis[N];

int judge(int x)
{
    if(x <=  && x >=  && !vis[x])
        return ;
    return -;
}

int BFS(int x)
{
    queue<node>Q;
    node now, next;
    now.x = x;
    now.step = ;
    vis[now.x] = true;
    Q.push(now);
    while(!Q.empty())
    {
        now = Q.front();
        Q.pop();
        if(now.x == n)
            return now.step;
        next.x = now.x + ;
        if(judge(next.x) == )
        {
            vis[next.x] = true;
            next.step = now.step + ;
            Q.push(next);
        }
        next.x = now.x - ;
        if(judge(next.x) == )
        {
            vis[next.x] = true;
            next.step = now.step + ;
            Q.push(next);
        }
        next.x = now.x * ;
        if(judge(next.x) == )
        {
            vis[next.x] = true;
            next.step = now.step + ;
            Q.push(next);
        }
    }
    return -;
}
int main()
{
    while(scanf("%d%d", &m, &n)!= EOF)
    {
        memset(vis, false, sizeof(vis));
        printf("%d\n", BFS(m));
    }
    return ;
}