POJ1985 DFS【STL__vector_的应用】

//#pragma comment(linker, "/STACK:16777216") //for c++ Compiler
#include <stdio.h>
#include <iostream>
#include <climits>
#include <cstring>
#include <stack>
#include <vector>
#include <algorithm>
#define ll long long
using namespace std;

const int INF = 0x3f3f3f3f;

struct edge{
    int ev,w;
    edge(int a,int b):ev(a),w(b){ }
};
vector <edge> elist[400000];
bool vis[400000];
int s, ans;

void DFS(int fv,int dis){
    if (dis > ans){
        ans = dis;
        s = fv;
    }
    vis[fv] = true;
    int size = elist[fv].size();

    int ev,w;
    for (int i = 0; i < size; ++i){
        ev = elist[fv][i].ev;
        w = elist[fv][i].w;
        if (vis[ev]) continue;
        DFS(ev,dis + w);
    }
}

int main(){
    int N,M;
    int fv,ev,w;
    char dir[10];
    while(EOF != scanf("%d%d",&N,&M)){
        for (int i = 1; i <= N; ++i)
            elist[i].clear();
        for (int i = 1; i <= M; ++i){
            scanf("%d%d%d%s",&fv,&ev,&w,dir);
            elist[fv].push_back(edge(ev,w));
            elist[ev].push_back(edge(fv,w));
        }

        memset(vis,0,sizeof(vis));
        s  = ans = 0;
        DFS(1,0);

        memset(vis,0,sizeof(vis));
        ans = 0;
        DFS(s,0);

        printf("%d\n",ans);
    }
    return 0;
}