poj 3268 最短路

#include<iostream>
#include<cstdio>
#include<cstring>
#include<queue>
#include<algorithm>
using namespace std;

const int maxn = 1005;
const int maxm = 100005;
const int INF = 0x3f3f3f3f;
int N,M,X;
int first[maxn];
int en;
int d[maxn],d1[maxn];
struct Edge{
    int u,v,w;
    int next;
    void assign(int a,int b,int c,int d){
        u = a;  v = b;  w = c;  next = d; 
    }
    bool operator <(const Edge& r)const {
        return w > r.w;
    }
}edge[maxm];
void Addedge(int a,int b,int c){
    int d = first[a];
    first[a] = en;
    edge[en++].assign(a,b,c,d);
}

void Dijkstra(int x,int n){
    priority_queue <Edge> Q;
    while(!Q.empty())  Q.pop(); 
    memset(d,0x3f,sizeof(d));
    int vis[maxn];
    memset(vis,0,sizeof(vis));
    Q.push((Edge){x,0,0});  d[x] = 0; 
    while(!Q.empty()){ 
        Edge e = Q.top() ; Q.pop() ; 
        int u = e.u; 
        if(vis[u]) continue;
        vis[u] = true;  
        for(int i=first[u];i!=-1;i=edge[i].next){  
            int v = edge[i].v;     
            if( d[v] > d[u] + edge[i].w){
                d[v] = d[u] + edge[i].w;    
                Q.push((Edge){v,0,d[v]}); 
            }
        }
    }
    
}
/*
void SPFA(int x,int n){
    queue<int> Q;
    memset(d,0x3f,sizeof(d));
    bool inq[maxn];
    memset(inq,0,sizeof(inq));
    int cnt[maxn];
    memset(cnt,0,sizeof(cnt));
    Q.push(x); inq[x] = true; cnt[x]++; d[x] = 0; 
    while(!Q.empty()){ 
        int u = Q.front() ; Q.pop() ; inq[u] = false;
        for(int i=first[u];i!=-1;i=edge[i].next){  
            int v = edge[i].v;      // printf("%d %d \n",v,inq[v]);
            if( d[v] > d[u] + edge[i].w){
                
                d[v] = d[u] + edge[i].w;    //printf("%d %d %d\n",v,u,d[v]);
                if(!inq[v]){
                 inq[v] = true;
                 Q.push(v);
                 cnt[v]++;    
                }
                if(cnt[v] > n) return;
            }
            
        }
    }
    
    
}*/
void init(){
   memset(first,-1,sizeof(first));
   en = 1;    
}

int main()
{
    //if(freopen("input.txt","r",stdin)== NULL)  {printf("Error\n"); exit(0);}
    
    cin>>N>>M>>X;
    int u[maxm],v[maxm],w[maxm];
    init();
    for(int i=1;i<=M;i++){
        cin>>u[i]>>v[i]>>w[i];
        Addedge(u[i],v[i],w[i]);
    }
    //SPFA(X,N);
    Dijkstra(X,N);
    for(int i=1;i<=N;i++)  d1[i] = d[i]; 
    init(); 
    for(int i=1;i<=M;i++){
        Addedge(v[i],u[i],w[i]);  
    }
    //SPFA(X,N);
    Dijkstra(X,N);
    int ans = 0;  
    for(int i=1;i<=N;i++)   ans = max(ans ,d[i] + d1[i]);
    printf("%d\n",ans);
}