Codeforces Beta Round #14 (Div. 2) D. Two Paths 树形dp

题目链接：这里
题意：给你一棵树，让你选择两条不相交的路径，使得长度的乘积最大。
解法：枚举删除哪条边，然后再跑树形dp就好了。(维护最长和次长就可以了)

//CF 14D#include <bits/stdc++.h>using namespace std;const int maxn = 206;vector <int> G[maxn];int n, maxlen;int dfs(int x, int fa){    int len1 = 0, len2 = 0, len = 0;    for(int i = 0; i < G[x].size(); i++){        int v = G[x][i];        if(v == fa) continue;        len = max(dfs(v, x), len);        if(maxlen > len1){            len2 = len1;            len1 = maxlen;        }        else{            len2 = max(len2, maxlen);        }    }    len = max(len, len1+len2);    maxlen = len1 + 1;    return len;}int main(){    scanf("%d", &n);    for(int i = 1; i < n; i++){        int u, v;        scanf("%d%d", &u, &v);        G[u].push_back(v);        G[v].push_back(u);    }    int ans = 0;    for(int i = 1; i <= n; i++){        for(int j = 0; j < G[i].size(); j++){            int a = dfs(G[i][j], i);            int b = dfs(i, G[i][j]);            ans = max(ans, a*b);        }    }    cout << ans << endl;    return 0;}