hdu1495（bfs）

题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=1495

题意：有三个杯子，开始时第一个杯子装满水（体积为a），倒来倒去，得到其中2个杯里的水的体积都为a/2，求最小次数，不存在就输出NO。

分析：因为被子没有刻度，所以倒入时要倒满或倒完才能保证知道容积，即有6种情况来分别遍历。

#include <iostream>
#include <cstdlib>
#include <queue>
#include <vector>
#include <cstdio>
#include <map>
#include <cstring>
#include <algorithm>
#define INF 100000000
#define maxn 111111
#define ll __int64
#define lson 1,m,rt<<1
#define rson m+1,r,rt<<1|1
using namespace std;
int vis[110][110][110];
int a,b,c,flag;
struct node
{
    int x,y,z;
    int step;
};
int judge(node k)
{
    if((k.x==k.y&&k.z==0)||(k.x==k.z&&k.y==0)||(k.y==k.z&&k.x==0))
        return 1;
    return 0;
}
void bfs()
{
    queue<node>que;
    node now,next;
    int num;
    now.x=a;now.y=0;
    now.z=0;now.step=0;
    vis[a][0][0]=1;
    que.push(now);
    while(!que.empty())
    {
        now=que.front();que.pop();
        if(judge(now))
        {
            printf("%d
",now.step);
            flag=1;
            return;
        }
        if(now.x>0)//a倒入其他
        {
            if(b>now.y)//a倒入b
            {
                num=b-now.y;
                next.z=now.z;
                next.step=now.step+1;
                if(now.x>num)//a倒不完
                {
                    next.x=now.x-num;
                    next.y=b;
                }
                else//倒完
                {
                    next.y=now.x+now.y;
                    next.x=0;
                }
                if(!vis[next.x][next.y][next.z])
                {
                    vis[next.x][next.y][next.z]=1;
                    que.push(next);
                }
            }
            if(c>now.z)//a倒入c
            {
                num=c-now.z;
                next.y=now.y;
                next.step=now.step+1;
                if(now.x>num)//倒不完
                {
                    next.x=now.x-num;
                    next.z=c;
                }
                else//倒完
                {
                    next.z=now.x+now.z;
                    next.x=0;
                }
                if(!vis[next.x][next.y][next.z])
                {
                    vis[next.x][next.y][next.z]=1;
                    que.push(next);
                }
            }
        }
        if(now.y>0)//b倒入其他
        {
            if(a>now.x)
            {
                num=a-now.x;
                next.z=now.z;
                next.step=now.step+1;
                if(now.y>num)
                {
                    next.y=now.y-num;
                    next.x=a;
                }
                else
                {
                    next.x=now.x+now.y;
                    next.y=0;
                }
                if(!vis[next.x][next.y][next.z])
                {
                    vis[next.x][next.y][next.z]=1;
                    que.push(next);
                }
            }
            if(c>now.z)
            {
                num=c-now.z;
                next.x=now.x;
                next.step=now.step+1;
                if(now.y>num)
                {
                    next.y=now.y-num;
                    next.z=c;
                }
                else
                {
                    next.z=now.y+now.z;
                    next.y=0;
                }
                if(!vis[next.x][next.y][next.z])
                {
                    vis[next.x][next.y][next.z]=1;
                    que.push(next);
                }
            }
        }
        if(now.z>0)//c倒入其他
        {
            if(b>now.y)
            {
                num=b-now.y;
                next.x=now.x;
                next.step=now.step+1;
                if(now.z>num)
                {
                    next.z=now.z-num;
                    next.y=b;
                }
                else
                {
                    next.y=now.z+now.y;
                    next.z=0;
                }
                if(!vis[next.x][next.y][next.z])
                {
                    vis[next.x][next.y][next.z]=1;
                    que.push(next);
                }
            }
            if(a>now.x)
            {
                num=a-now.x;
                next.y=now.y;
                next.step=now.step+1;
                if(now.z>num)
                {
                    next.z=now.z-num;
                    next.x=a;
                }
                else
                {
                    next.x=now.x+now.z;
                    next.z=0;
                }
                if(!vis[next.x][next.y][next.z])
                {
                    vis[next.x][next.y][next.z]=1;
                    que.push(next);
                }
            }
        }
    }
}
int main()
{
    while(scanf("%d%d%d",&a,&b,&c)>0)
    {
        if(a+b+c==0)break;
        if(a%2)//剪枝
        {
            puts("NO");
            continue;
        }
        memset(vis,0,sizeof(vis));
        flag=0;
        bfs();
        if(!flag)puts("NO");
    }
}