【BFS】Pots

[poj3414]Pots

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 16925		Accepted: 7168		Special Judge

Description

You are given two pots, having the volume of A and B liters respectively. The following operations can be performed:

1. FILL(i)        fill the pot i (1 ≤ i ≤ 2) from the tap;
2. DROP(i)      empty the pot i to the drain;
3. POUR(i,j)    pour from pot i to pot j; after this operation either the pot j is full (and there may be some water left in the pot i), or the pot i is empty (and all its contents have been moved to the pot j).

Write a program to find the shortest possible sequence of these operations that will yield exactly C liters of water in one of the pots.

Input

On the first and only line are the numbers A, B, and C. These are all integers in the range from 1 to 100 and C≤max(A,B).

Output

The first line of the output must contain the length of the sequence of operations K. The following K lines must each describe one operation. If there are several sequences of minimal length, output any one of them. If the desired result can’t be achieved, the first and only line of the file must contain the word ‘impossible’.

Sample Input

3 5 4

Sample Output

6
FILL(2)
POUR(2,1)
DROP(1)
POUR(2,1)
FILL(2)
POUR(2,1)

Source

题目大意：两只杯子，分别N容量M容量，问要怎样凑出K容量

                DROP(x)：倒空x杯

                FILL(x):倒满x被

                POUR(x,y)：将x杯中的水倒入y

试题分析：思路很明确的一道题，直接写就行，就算锻炼代码能力了  难得1AC

代码

#include<iostream>
#include<cstring>
#include<cstdio>
#include<queue>
#include<stack>
#include<vector>
#include<algorithm>
//#include<cmath>

using namespace std;
const int INF = 9999999;
#define LL long long

inline int read(){
	int x=0,f=1;char c=getchar();
	for(;!isdigit(c);c=getchar()) if(c=='-') f=-1;
	for(;isdigit(c);c=getchar()) x=x*10+c-'0';
	return x*f;
}
int N,M,K;
struct data{
	int a,b,fr,st;
    int fg;
}Que[200001];
int l=1,r=1;
/*
1:Fill(1)
2:Fill(2)
3:POUR(1,2)
4:ROUP(2,1)
5:DROP(1)
6:DROP(2)
*/
bool vis[201][201];
bool alflag=false;

void print(data k){
	if(k.fr!=-1){
		print(Que[k.fr]);
		if(k.fg==1) puts("FILL(1)");
		if(k.fg==2) puts("FILL(2)");
		if(k.fg==3) puts("POUR(1,2)");
		if(k.fg==4) puts("POUR(2,1)");
		if(k.fg==5) puts("DROP(1)");
		if(k.fg==6) puts("DROP(2)");
	}
}

void BFS(){
	Que[l].a=0,Que[l].b=0,Que[l].fr=-1,Que[l].st=0;
	vis[0][0]=true;
	int x,y,step;
	while(l<=r){
		x=Que[l].a,y=Que[l].b,step=Que[l].st;
		if(x!=N&&!vis[N][y]){
			vis[N][y]=true;
			Que[++r].fg=1;
			Que[r].a=N;
			Que[r].b=y;
			Que[r].st=step+1;
			Que[r].fr=l;
			if(Que[r].a==K||Que[r].b==K){
				printf("%d\n",step+1);
				print(Que[r]);
				alflag=true;
				return ;
			}
		}
		if(y!=M&&!vis[x][M]){
			vis[x][M]=true;
			Que[++r].fg=2;
			Que[r].a=x;
			Que[r].b=M;
			Que[r].st=step+1;
			Que[r].fr=l;
			if(Que[r].a==K||Que[r].b==K){
				printf("%d\n",step+1);
				print(Que[r]);
				alflag=true;
				return ;
			}
		}
		if(x&&y!=M){
			int xx,yy;
			if(x-(M-y)<=0) yy=y+x,xx=0;
			else yy=M,xx=x-(M-y);
			if(!vis[xx][yy]){
			    vis[xx][yy]=true;
			    Que[++r].fg=3;
		    	Que[r].a=xx;
		    	Que[r].b=yy;
		    	Que[r].st=step+1;
	    		Que[r].fr=l;
	    		if(Que[r].a==K||Que[r].b==K){
					printf("%d\n",step+1);
					print(Que[r]);
					alflag=true;
					return ;
				}
	    	}
		}
		if(y&&x!=N){
			int xx,yy;
			if(y-(N-x)<=0) xx=y+x,yy=0;
			else xx=N,yy=y-(N-x);
			if(!vis[xx][yy]){
			    vis[xx][yy]=true;
			    Que[++r].fg=4;
		    	Que[r].a=xx;
		    	Que[r].b=yy;
		    	Que[r].st=step+1;
	    		Que[r].fr=l;
	    		if(Que[r].a==K||Que[r].b==K){
				    printf("%d\n",step+1);
			    	print(Que[r]);
			    	alflag=true;
			    	return ;
			    }
	    	}
		}
		if(x&&!vis[0][y]){
			vis[0][y]=true;
			Que[++r].fg=5;
			Que[r].a=0;
			Que[r].b=y;
			Que[r].st=step+1;
			Que[r].fr=l;
			if(Que[r].a==K||Que[r].b==K){
				printf("%d\n",step+1);
				print(Que[r]);
				alflag=true;
				return ;
			}
		}
		if(y&&!vis[x][0]){
			vis[x][0]=true;
			Que[++r].fg=6;
			Que[r].a=x;
			Que[r].b=0;
			Que[r].st=step+1;
			Que[r].fr=l;
			if(Que[r].a==K||Que[r].b==K){
				printf("%d\n",step+1);
				print(Que[r]);
				alflag=true;
				return ;
			}
		}
		l++;
	}
}

int main(){
	//freopen(".in","r",stdin);
	//freopen(".out","w",stdout);
	N=read(),M=read(),K=read();
	BFS();
	if(!alflag){
		printf("impossible");
		return 0;
	}
	return 0;
}