sol 1：S建立反向图

#include <bits/stdc++.h>
using namespace std;
const int N = 2e4 + 100, INF = 0x3f3f3f3f;
int a[N], ne[N], h[N], e[N], dis[N], idx;
bool st[N];
int w[N],n,m,s;
typedef pair<int, int> PII;
void add(int a, int b, int c)
{
    e[idx] = b, w[idx] = c, ne[idx] = h[a], h[a] = idx++;
}
void dij(int s)
{
    memset(dis, 0x3f, sizeof dis);
    memset(st, 0, sizeof st);
    dis[s] = 0;
    priority_queue<PII, vector<PII>, greater<PII>> heap;
    heap.push({0, s});
    while (!heap.empty())
    {
        auto t = heap.top();
        heap.pop();
        int ver = t.second,distance=t.first;
        if (st[ver])
            continue;
        st[ver] = 1;
        for (int i = h[ver]; ~i; i = ne[i])
        {
            int j=e[i];
            if (dis[j] > distance + w[i])
            {
                dis[j] = distance + w[i];
                heap.push({dis[j], j});
            }
        }
    }
}
int main()
{
    ios::sync_with_stdio(false);
    while (cin >> n >> m >> s)
    {
        idx=0;
        memset(h, -1, sizeof h);
        while (m--)
        {
            int a, b, c;
            cin >> a >> b >> c;
            add(b, a, c);
        }
        int k;
        cin >> k;
        for (int i = 1; i <= k; i++)
            cin >> a[i];
        dij(s);
        int res = INF;
        for (int i = 1; i <= k; i++)        
            res = min(res, dis[a[i]]);
        if (res==INF) cout<<"-1\n";
        else cout<<res<<endl;
    }

    return 0;
}

sol 2:建立虚拟源点(dij)

#include<bits/stdc++.h>
using namespace std;
const int N = 2e5 + 100, INF = 0x3f3f3f3f;
int a[N], ne[N], h[N], e[N], dis[N], idx;
bool st[N];
int w[N],n,m,s;
typedef pair<int, int> PII;
void add(int a,int b,int c)
{
    e[idx]=b,w[idx]=c,ne[idx]=h[a],h[a]=idx++;
}
void dij()
{
    memset(st,0,sizeof st);
    memset(dis,0x3f,sizeof dis);
    priority_queue<PII,vector<PII>,greater<PII> > heap;
    heap.push({0,0});
    dis[0]=0;
    while(!heap.empty())
    {
        auto t=heap.top();
        heap.pop();
        int ver=t.second,distance=t.first;
        for(int i=h[ver];~i;i=ne[i])
        {
            int j=e[i];
            if (dis[j]>distance+w[i])
            {
                dis[j]=distance + w[i];
                heap.push({dis[j],j});
            }
        }
    }
}
int main(){
    ios::sync_with_stdio(false);
    while (cin >> n >> m >> s)
    {
        idx=0;
        memset(h, -1, sizeof h);
        while (m--)
        {
            int a, b, c;
            cin >> a >> b >> c;
            add(a, b, c);
        }
        int k;
        cin >> k;
        for (int i = 1; i <= k; i++)
        {
            int b;
            cin>>b;
            add(0,b,0);
        }
        dij();
        int res = dis[s];

        if (res==INF) cout<<"-1\n";
        else cout<<res<<endl;
    }

    return 0;
}

sol 3虚拟源点+spfa

#include<bits/stdc++.h>
using namespace std;
const int N = 2e5 + 100, INF = 0x3f3f3f3f;
int a[N], ne[N], h[N], e[N], dis[N], idx;
bool st[N];
int w[N],n,m,s;
typedef pair<int, int> PII;
void add(int a,int b,int c)
{
    e[idx]=b,w[idx]=c,ne[idx]=h[a],h[a]=idx++;
}
void spfa()
{
    memset(st,0,sizeof st);
    memset(dis,0x3f,sizeof dis);
    queue<int> q;
    q.push(0);
    dis[0]=0;
    while(!q.empty())
    {
        auto t=q.front();
        q.pop();
        st[t]=0;
        for(int i=h[t];~i;i=ne[i])
        {
            int j=e[i];
            if (dis[j]>dis[t]+w[i])
            {
                dis[j]=dis[t] + w[i];
                if (!st[j])
                {
                    q.push(j);
                    st[j]=1;
                }
            }
        }
    }
}
int main(){
    ios::sync_with_stdio(false);
    while (cin >> n >> m >> s)
    {
        idx=0;
        memset(h, -1, sizeof h);
        while (m--)
        {
            int a, b, c;
            cin >> a >> b >> c;
            add(a, b, c);
        }
        int k;
        cin >> k;
        for (int i = 1; i <= k; i++)
        {
            int b;
            cin>>b;
            add(0,b,0);
        }
        spfa();
        int res = dis[s];

        if (res==INF) cout<<"-1\n";
        else cout<<res<<endl;
    }

    return 0;
}