PKU 3414 【裸BFS】

bfs,主要是用pre记录前驱，输出路径。

#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>
const int N = 100+10;
using namespace std;
bool mark[N][N];
int ans[999999];
int va ,vb,c;
int cnt=0;
struct state
{
    int x,y;
    int op;
    int d;
    int pre;
    state(int xx,int yy,int opp,int dd,int pree):x(xx),y(yy),op(opp),d(dd),pre(pree)
    {
    }
    state()
    {
    }
};
state q[10010];
int res[10010];
void output(int i)
{
    int pre = i;
    while (pre!=-1)
    {
        res[cnt++] = pre;
        pre = q[pre].pre;
    }
    printf("%d\n",cnt-1);
    for (int i=cnt-1;i>=0;i--)
    {
        switch (q[res[i]].op)
        {

        case 0:
            printf("FILL(%d)\n",q[res[i]].d);
            break;
        case 1:
            printf("DROP(%d)\n",q[res[i]].d);
            break;
        case 2:
            if (q[res[i]].d==1)
            {
                printf("POUR(1,2)\n");
            }
            else
            {
                printf("POUR(2,1)\n");
            }
            break;

        }

    }

}
void bfs()
{
    int front=-1,rear=-1;
    bool flag = false;
    state cur;
    memset(mark,false,sizeof(mark));
    q[++rear] = state(0,0,-1,-1,-1);
    while (front<rear)
    {
        int tx,ty,tpre;
        cur  = q[++front];
        tx = cur.x;
        ty = cur.y;
        tpre = front;
        if (mark[tx][ty])
        {
            continue;
        }
        else
        {
            mark[tx][ty] = true;
        }
        if (tx==c||ty==c)
        {
            flag = true;
            break;
        }
        q[++rear] = state(va,ty,0,1,tpre);
        q[++rear] = state(tx,vb,0,2,tpre);
        if (tx!=0)
        {
            q[++rear] = state(0,ty,1,1,tpre);
            int t = vb - ty;
            if (tx-t<0)
            {
                q[++rear] = state(0,ty+tx,2,1,tpre);
            }
            else
            {
                q[++rear] = state(tx-t,vb,2,1,tpre);
            }

        }
        if (ty!=0)
        {
            q[++rear] = state(tx,0,1,2,tpre);
            int t = va - tx;
            if (ty-t<0)
            {
                q[++rear] = state(tx+ty,0,2,2,tpre);
            }
            else
            {
                q[++rear] = state(va,ty-t,2,2,tpre);
            }
        }

    }
    if (flag)
    {
        output(front);
    }
    else
    {
        printf("impossible\n");
    }

}
int main()
{
    scanf("%d%d%d",&va,&vb,&c);
    bfs();

    return 0;
}