[POJ1985] Cow Marathon 「树的直径」

>传送门<

题意：求树的直径

思路：就是道模板题，两遍dfs就求出来了

Code

#include <cstdio>
#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;
typedef pair<int, int> P;

const int MAX_N = 1000005;
vector<P> G[MAX_N];
int n, m, s, ans;
int u, v, val;
char ch;

void dfs(int u, int pre, int step)
{
    if (ans<step) ans = step, s = u;
    for (int i = 0; i < G[u].size(); i++) {
        int v = G[u][i].first, val = G[u][i].second;
        if (v!=pre) dfs(v, u, step+val);
    }
}
int main() 
{
    scanf("%d%d", &n, &m);
    for (int i = 1; i <= m; i++) {
        scanf("%d %d %d %c", &u, &v, &val, &ch);
        G[u].push_back(P(v, val));
        G[v].push_back(P(u,val));
    }
    dfs(1, 0, 0);
    dfs(s, 0, 0);
    printf("%d", ans);
}