AtCoder Beginner Contest 132 E

bfs

位置+状态

just need to calculate min value(only it is useful), so O(1*x)

挺有趣的一道题。。。

#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <cstring>
#include <string>
#include <algorithm>
#include <iostream>
using namespace std;
#define ll long long

const int maxn=1e6+10;

struct node
{
    int d;
    node *to;
}*e[maxn];

int qx[maxn*3],qy[maxn*3],qz[maxn*3];

int f[maxn][3];

int main()
{
    node *p;
    int n,m,x,y,z,xx,yy,zz,head,tail,s,t;
    scanf("%d%d",&n,&m);
    while (m--)
    {
        scanf("%d%d",&x,&y);
        p=new node();
        p->d=y;
        p->to=e[x];
        e[x]=p;
    }

    scanf("%d%d",&s,&t);
    qx[1]=s,qy[1]=0,qz[1]=3;
    head=0,tail=1;
    while (head<tail)
    {
        head++;
        x=qx[head];
        y=qy[head];
        z=qz[head];

        p=e[x];
        while (p)
        {
            xx=p->d;
            yy=(y+1)%3;
            zz=z+1;
            if (!f[xx][yy])
            {
                if (xx==t && yy==0)
                {
                    printf("%d",(zz-3)/3);
                    return 0;
                }
                tail++;
                qx[tail]=xx;
                qy[tail]=yy;
                qz[tail]=zz;
                f[xx][yy]=zz;
            }
            p=p->to;
        }
    }
    printf("-1");
    return 0;
}