【codeforces 764C】Timofey and a tree 題解

題目

題目連結：http://codeforces.com/problemset/problem/764/C

C. Timofey and a tree time limit per test 2 seconds memory limit per test 256 megabytes input standard input output standard output

Each New Year Timofey and his friends cut down a tree of n vertices and bring it home. After that they paint all the n its vertices, so that the i-th vertex gets color ci.

Now it’s time for Timofey birthday, and his mother asked him to remove the tree. Timofey removes the tree in the following way: he takes some vertex in hands, while all the other vertices move down so that the tree becomes rooted at the chosen vertex. After that Timofey brings the tree to a trash can.

Timofey doesn’t like it when many colors are mixing together. A subtree annoys him if there are vertices of different color in it. Timofey wants to find a vertex which he should take in hands so that there are no subtrees that annoy him. He doesn’t consider the whole tree as a subtree since he can’t see the color of the root vertex.

A subtree of some vertex is a subgraph containing that vertex and all its descendants.

Your task is to determine if there is a vertex, taking which in hands Timofey wouldn’t be annoyed.

Input

The first line contains single integer n (2 ≤ n ≤ 105) — the number of vertices in the tree.

Each of the next n - 1 lines contains two integers u and v (1 ≤ u, v ≤ n, u ≠ v), denoting there is an edge between vertices u and v. It is guaranteed that the given graph is a tree.

The next line contains n integers c1, c2, …, cn (1 ≤ ci ≤ 105), denoting the colors of the vertices.

Output

Print “NO” in a single line, if Timofey can’t take the tree in such a way that it doesn’t annoy him.

Otherwise print “YES” in the first line. In the second line print the index of the vertex which Timofey should take in hands. If there are multiple answers, print any of them.

Examples Input

4
1 2
2 3
3 4
1 2 1 1
      

Output

YES
2      

Input

3
1 2
2 3
1 2 3
      

Output

YES
2      

Input

4
1 2
2 3
3 4
1 2 1 2
      

Output

NO      

題目大意

給一顆帶顔色的樹，看能不能找一個頂點，使其每一個子樹的頂點的顔色都相同。

題解

bfs搜尋。

順序嘗試頂點，看看這個頂點是否符合題目要求。

第一次寫的時候沒剪枝，結果毫無疑問TLE了。加了個記憶化搜尋，記錄下已經搜尋過的點，就過了。詳細看代碼。

代碼

//2017-02-02-22.30
//C

#include <bits/stdc++.h>
using namespace std;

vector<int> d[ + ];
int c[ + ];
int rt, n;
map<pair<int, int>, bool> m;
bool bfs(int i, int fa)
{
    if (m.find({i, fa}) != m.end()) return m[{i, fa}];
    vector<int>::iterator it;
    //printf(" %d %d\n", i, fa);
    for (it = d[i].begin(); it != d[i].end(); it++)
    {
        if (*it == fa) continue;
        if ((fa == - || c[i] == c[*it]) && bfs(*it, i)) {continue;}
        else {m.insert({{i, fa}, }); return ;}
    }
    m.insert({{i, fa}, });
    return ;
}

int main()
{
    scanf("%d", &n);
    for (int i = ; i < n - ; i++)
    {
        int u, v;
        scanf("%d%d", &u, &v);
        d[u].push_back(v);
        d[v].push_back(u);
    }
    for (int i = ; i <= n; i++)
    {
        scanf("%d", &c[i]);
    }
    for (int i = ; i <= n; i++)
    {
        if (bfs(i, -))
        {
            printf("YES\n%d\n", i);
            return ;
        }
    }
    puts("NO");
}