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\n",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");

    }

}

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