[kuangbin带你飞]专题四 最短路练习

#include<iostream>
#include<cstring>
#include<algorithm>
#include<iomanip>
#include<cmath>
#include<cstdio>
#include<vector>
#include<string>
#include<map>
#include<queue>
#include<vector>
using namespace std;
/*
单源最短路 路径方向与switch方向同向那么路径权值0，否则为1
*/
#define MAXN 101
#define INF 0x3f3f3f3f
bool g[MAXN][MAXN],TO[MAXN][MAXN],been[MAXN];
int lowcost[MAXN],A,B,N;
int Dijkstra(int beg,int to)
{
    for(int i=1;i<=N;i++)
    {
        lowcost[i] = INF;
        been[i] = false;
    }
    lowcost[beg] = 0;
    for(int i=0;i<N;i++)
    {
        int Minc = INF,k = -1;
        for(int j=1;j<=N;j++)
        {
            if(!been[j]&&lowcost[j]<Minc)
            {
                Minc = lowcost[j];
                k = j;
            }
        }
        if(k==-1) break;
        been[k] = true;
        for(int j=1;j<=N;j++)
        {
            int cost;
            if(!g[k][j]) cost = INF;
            else
            {
                if(TO[k][j]==true) 
                    cost = 0;
                else cost = 1;
            }
            if(!been[j]&&lowcost[j]>lowcost[k]+cost)
            {
                lowcost[j] = lowcost[k]+cost;
            }
        }
    }
    return lowcost[to];
}
int main()
{
    cin>>N>>A>>B;
    int k,tmp;
    for(int i=1;i<=N;i++)
    {
        cin>>k;
        for(int j=1;j<=k;j++)
        {
            cin>>tmp;
            if(j==1)
                TO[i][tmp] = true;
            g[i][tmp] = true;
        }
    }
    int ans = Dijkstra(A,B);
    if(ans!=INF)
        cout<<ans<<endl;
    else
        cout<<-1<<endl;
    return 0;
}