ληστεία 2017-2018

#include <iostream>
#include <vector>
#include <queue>
using namespace std;
typedef pair<int, int> ii;
typedef vector<int> vi;
typedef vector<ii> vii;
vector<vii> AdjList;
vector<vii> AdjList1;
priority_queue< ii, vector<ii>, greater<ii> > pq;
vi dist;
#define INF 1000005
void dijkstra1(int s){
        dist[s] = 0;
        pq.push(ii(0, s));
        while (!pq.empty()) {
                ii front = pq.top();
                pq.pop();
                int w = front.first;
                int u = front.second;
                if (w > dist[u]){
                        continue;
                     }
                for (int j = 0; j < AdjList1[u].size(); j++) {
                     ii v = AdjList1[u][j];
                        if (dist[u] + v.second < dist[v.first]) {
                                dist[v.first] = dist[u] + v.second;
                              pq.push(ii(dist[v.first], v.first));
                        }
              }
        }
}
void dijkstra(int s){
        dist[s] = 0;
        pq.push(ii(0, s));
        while (!pq.empty()) {
                ii front = pq.top();
                pq.pop();
                int w = front.first;
                int u = front.second;
                if (w > dist[u]){
                        continue;
                     }
                for (int j = 0; j < AdjList[u].size(); j++) {
                     ii v = AdjList[u][j];
                        if (dist[u] + v.second < dist[v.first]) {
                                dist[v.first] = dist[u] + v.second;
                              pq.push(ii(dist[v.first], v.first));
                        }
              }
        }
}
int main() {
        int V, E, s, a, b, w;
        int A;
        long long q=INF;
        cin >> V >> E >> A;
        cin>>s;
        int y[V];
        AdjList.assign(V, vii());
        AdjList1.assign(V,vii());
        dist.assign(V, INF);
        for (int i = 0; i < E; i++) {
                 cin >> a >> b >> w;
                AdjList[a].push_back(ii(b, w));
                AdjList1[b].push_back(ii(a, w));
        }
        dijkstra(A);
        for (int i = 0; i < V; i++){
                y[i] = y[i] + dist[i];
        }
        dist.assign(V, INF);
       dijkstra(s);
        for (int i = 0; i < V; i++){
            y[i] = dist[i];
        }
        dist.assign(V, INF);
        dijkstra1(A);
         for (int i = 0; i < V; i++){
                 y[i] = y[i] + dist[i];
         }
        dist.assign(V, INF);
        dijkstra1(s);
        for (int i = 0; i < V; i++){
            y[i] = dist[i];
        }
       for(int i=0;i<V;i++){
                if(q < y[i]){
                        q = y[i];
               }
        }
        cout<<q<<endl;
return 0;
}