树上行走

树上行走

思路
用并查集维护集合个数，找到最大的集合，从小到大输出集合里面的元素，若有多个最大集合，从小到大依次输出。
code

#include<bits/stdc++.h>
using namespace std;
const int N = 2e5+5;
int fa[N], val[N], n, son[N];
void init(int n)
{
    for(int i = 1; i <= n; i++)
        fa[i] = i, son[i] = 1;
}
int find(int x)
{
    return x == fa[x] ? x : fa[x] = find(fa[x]);
}
void merge(int x, int y)
{
    int fx = find(x), fy = find(y);
    if(fx != fy)
        fa[fx] = fy, son[fy] += son[fx];
}
int main()
{
    scanf("%d", &n);
    init(n);
    for(int i = 1; i <= n; i++)
        scanf("%d", &val[i]);
    int cnt = 1;
    for(int i = 1; i <= n-1; i++)
    {
        int u, v;
        scanf("%d%d", &u, &v);
        if(val[u] == val[v])
            merge(u, v), cnt = max(cnt, son[find(v)]);
        /*cout << cnt << endl;
        system("pause");*/
    }
    int num = 0;
    for(int i = 1; i <= n; i++)
        if(son[find(i)] == cnt)
            num++;
    cout << num << endl;
    for(int i = 1; i <= n; i++)
        if(cnt == son[find(i)])
        cout << i << ' ';
    //system("pause");
    return 0;
}