HackerEarth Separating Numbers problem solution

#include <iostream>
#include <vector>
#include <algorithm>
#include <fstream>
#include <queue>
#include <deque>
#include <iomanip>
#include <cmath>
#include <set>
#include <stack>
#include <map>
#include <unordered_map>

#define FOR(i,n) for(int i=0;i<n;i++)
#define FORE(i,a,b) for(int i=a;i<=b;i++)
#define ll long long 
//#define int long long
#define ld long double
#define vi deque<int>
#define pb push_back
#define ff first
#define ss second
#define ii pair<int,int>
#define iii pair<int,ii>
#define il pair<int,ll>
#define pll pair<ll,ll>
#define _path pair<ll,pair<ll,int> > 
#define vv deque
//#define endl 'n'
//#define mp make_pair

using namespace std;

const int MAXN = 3e5+5;
const ll INF = 1e18;

vi g[MAXN];

struct DSU{
    int parent[MAXN];
    int sz[MAXN];
    map<int,ll> mp[MAXN];
    DSU(int* arr,int n){
        FOR(i,n)parent[i] = i;
        FOR(i,n)sz[i] = 1;
        FOR(i,n)mp[i][arr[i]] = 1;
    }

    int find(int a){
        if(parent[a] != a)parent[a] = find(parent[a]);
        return parent[a];
    }

    ll merge(int a,int b){
        int pa = find(a);
        int pb = find(b);
        ll sum = 0;
        if(sz[pa] < sz[pb])swap(pa,pb);
        for(auto e: mp[pb]){
            sum += e.ss*mp[pa][e.ff];
            mp[pa][e.ff] += e.ss;
        }
        sz[pa] += sz[pb];
        parent[pb] = pa;
        mp[pb].clear();
        return sum;
    }
};

void solve(){
    int n,q;
    cin >> n;
    q = n-1;
    ii edge[n];
    FOR(i,n-1){
        int a,b;
        cin >> a >> b;
        a--;b--;
        g[a].pb(b);
        g[b].pb(a);
        edge[i] = {a,b};
    }
    int colors[n];
    FOR(i,n)cin >> colors[i];
    DSU dsu(colors,n);
    int queries[q];
    FOR(i,q){
        int x;
        cin >> x;
        x--;
        queries[i] = x;
    }
    ll ans[q];
    for(int i = q-1;i >= 0;i--){
        ans[i] = dsu.merge(edge[queries[i]].ff,edge[queries[i]].ss);
    }
    FOR(i,q){
        cout << ans[i] << endl;
    }
}


int main(){
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    
    int t = 1;
    while(t--){
        solve();
    }
    return 0;
}