POJ 3414 Pot (输出路径)【BFS】

#include <cstdio>
#include <cstring>

int v[5],m;

const int maxn=100000;
int vis[110][110];
int flag;

struct node{
    int val[5];
    int step;
    int pre;     //记录上一个点在que[]数组中的位置 
    node(int a=0,int b=0,int c=0,int d=-1){
        val[1]=a,val[2]=b,step=c,pre=d;
    }
}que[maxn];
 
 void fill(node &now,int a){
    now.val[a]=v[a];
}

void drop(node &now,int a){
    now.val[a]=0;
}

void pour(node &now,int a,int b){
    int sum=now.val[a]+now.val[b];
    if(sum>v[b]){
        now.val[b]=v[b];
        now.val[a]=sum-v[b];
    }
    else{
        now.val[b]=sum;
        now.val[a]=0;
    }
}

void print(node tmp){         //根据相邻两个点的状况来推断操作
    if(tmp.pre!=-1){
        print(que[tmp.pre]);
    }
    if(tmp.pre!=-1){       //如果这个点和上一个点之间有操作,就可以将这个操作求出来 
        node prenode=que[tmp.pre];
        node cal=prenode;    
        pour(cal,1,2);
        if(tmp.val[1]==v[1]&&tmp.val[2]==prenode.val[2]){
            printf("FILL(1)\n");
        }
        else if(tmp.val[2]==v[2]&&tmp.val[1]==prenode.val[1]){
            printf("FILL(2)\n");
        }
        else if(tmp.val[1]==0&&tmp.val[2]==prenode.val[2]){
            printf("DROP(1)\n");
        }
        else if(tmp.val[2]==0&&tmp.val[1]==prenode.val[1]){
            printf("DROP(2)\n");
        }
        else if(cal.val[1]==tmp.val[1]&&cal.val[2]==tmp.val[2]){
            printf("POUR(1,2)\n");
        }
        else{
            printf("POUR(2,1)\n");
        }
    }
}

void bfs(){
    memset(vis,0,sizeof(vis));
    int front=0,end=0;
    vis[0][0]=1;
    que[end++]=node(0,0,0,-1);
    while(front<end){
        node now=que[front];
        front++;
        if(now.val[1]==m||now.val[2]==m){
            flag=true;
            printf("%d\n",now.step);
            print(now);
            return;
        }
        for(int i=1;i<=2;i++){        //装满 
            node tmp=now;  //注意，这里为了防止now发生改变，从而对后面的操作产生影响，所以这里是对tmp进行操作 
            fill(tmp,i);
            if(!vis[tmp.val[1]][tmp.val[2]]){
                vis[tmp.val[1]][tmp.val[2]]=1;
                que[end++]=node(tmp.val[1],tmp.val[2],tmp.step+1,front-1);
            }
        }
        for(int i=1;i<=2;i++){        //倒空 
            node tmp=now;
            drop(tmp,i);
            if(!vis[tmp.val[1]][tmp.val[2]]){
                vis[tmp.val[1]][tmp.val[2]]=1;
                que[end++]=node(tmp.val[1],tmp.val[2],tmp.step+1,front-1);
            }
        }
        for(int i=1;i<=2;i++){       //i向j注水 
            for(int j=1;j<=2;j++){
                if(i==j)continue;
                node tmp=now;
                pour(tmp,i,j);
                if(!vis[tmp.val[1]][tmp.val[2]]){
                    vis[tmp.val[1]][tmp.val[2]]=1;
                    que[end++]=node(tmp.val[1],tmp.val[2],tmp.step+1,front-1);
                }
            }
        }
    }
}

int main(){
    while(scanf("%d %d %d",&v[1],&v[2],&m)!=EOF){
        flag=false;
        bfs();
        if(!flag){
            printf("impossible\n");
        }
    }
    return 0;
}