广搜最短路径变形，(POJ3414)

题目链接：http://poj.org/problem?id=3414

解题报告：

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

struct Node
{
    int a,b,step;
    char str[111][111];
};

int A,B,C;
bool mark[111][111];
bool bfs()
{
    memset(mark,false,sizeof(mark));
    queue<Node>que;
    Node p,q;
    p.a=0,p.b=0,p.step=0;
    que.push(p);
    mark[0][0]=true;
    while(!que.empty())
    {
        p=que.front();
        que.pop();
        if(p.a==C||p.b==C)
        {
            printf("%d\n",p.step);
            for(int i=1; i<=p.step; i++)
            {
                printf("%s\n",p.str[i]);
            }
            return true;
        }
        if(p.a==0)
        {
            q=p;
            q.a=A;
            q.step++;
            strcpy(q.str[q.step],"FILL(1)");
            if(!mark[q.a][q.b])
            {
                mark[q.a][q.b]=true;
                que.push(q);
            }
        }
        else if(p.a<=A)
        {
            q=p;
            q.a=0;
            q.step++;
            strcpy(q.str[q.step],"DROP(1)");
            if(!mark[q.a][q.b])
            {
                mark[q.a][q.b]=true;
                que.push(q);
            }
            if(p.b<B)
            {
                q=p;
                if(q.a+q.b<=B)
                {
                    q.b+=q.a;
                    q.a=0;
                }
                else
                {
                    q.a=(q.b+q.a)-B;
                    q.b=B;
                }
                q.step++;
                strcpy(q.str[q.step],"POUR(1,2)");
                if(!mark[q.a][q.b])
                {
                    mark[q.a][q.b]=true;
                    que.push(q);
                }
            }
        }
        if(p.b==0)
        {
            q=p;
            q.b=B;
            q.step++;
            strcpy(q.str[q.step],"FILL(2)");
            if(!mark[q.a][q.b])
            {
                mark[q.a][q.b]=true;
                que.push(q);
            }
        }
        else if(p.b<=B)
        {
            q=p;
            q.b=0;
            q.step++;
            strcpy(q.str[q.step],"DROP(2)");
            if(!mark[q.a][q.b])
            {
                mark[q.a][q.b]=true;
                que.push(q);
            }
            if(p.a<A)
            {
                q=p;
                if(q.b+q.a<=A)
                {
                    q.a+=q.b;
                    q.b=0;
                }
                else
                {
                    q.b=(q.b+q.a)-A;
                    q.a=A;
                }
                q.step++;
                strcpy(q.str[q.step],"POUR(2,1)");
                if(!mark[q.a][q.b])
                {
                    mark[q.a][q.b]=true;
                    que.push(q);
                }
            }
        }
    }
    return false;
}

int main()
{
    while(~scanf("%d%d%d",&A,&B,&C))
    {
        if(!bfs())puts("impossible");
    }
    return 0;
}