Problem F: tmk找三角

传送门：http://gdutcode.sinaapp.com/problem.php?cid=1057&pid=5

解题思路：

现在还不会。等几天在看一下。

实现代码：

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

const int N = 1e5+10;
int n;
int tot, head[N], to[N<<1], nex[N<<1], len[N<<1]; 
int f[N], dis[N], dep[N];

void init()
{
    tot = 0;
    for(int i = 0; i <= n; ++ i)
    {
        head[i] = -1;
    }
}

void addEdge(int x, int y, int l)
{
    to[tot] = y;
    len[tot] = l;
    nex[tot] = head[x];
    head[x] = tot++;
}

void dfs(int u, int d)
{
    dep[u] = d;
    for(int i = head[u]; ~i; i = nex[i])
    {
        int v = to[i];
        if(v == f[u]) continue;
        dis[v] = len[i];
        f[v] = u;
        dfs(v, d+1);
    }
}

bool solve(int x, int y)
{
    vector<int> vec;
    while(vec.size() < 50 && x != y)
    {
        if(dep[x] < dep[y])
        {
            vec.push_back(dis[y]);
            y = f[y];
        }
        else
        {
            vec.push_back(dis[x]);
            x = f[x];
        }
    }
    if(vec.size()>=50) return true;
    sort(vec.begin(), vec.end());
    for(int i = 0; i + 2 < vec.size(); ++ i)
    {
        if(vec[i] + vec[i+1] > vec[i+2]) return true;
    }
    return false;
}

int main()
{
    int T;
    scanf("%d", &T);
    while(T--)
    {
        scanf("%d", &n);
        init();
        for(int i = 1; i < n; ++ i)
        {
            int x, y, l;
            scanf("%d%d%d", &x, &y, &l);
            addEdge(x, y, l);
            addEdge(y, x, l);
        }
        dfs(1, 0);
        int m;
        scanf("%d", &m);
        for(int i = 0; i < m; ++ i)
        {
            int x, y;
            scanf("%d%d", &x, &y);
            puts(solve(x, y) ? "Yes" : "No");
        }
    }
    return 0;
}