网址 https://codeforces.com/edu/course/2/lesson/7/1/practice/contest/289390/problem/C

#include <bits/stdc++.h>

using namespace std;

int n,m;

vector<int> fa,siz,ex;
vector<vector<int> > son;

void init (int n) {
	fa.resize(n + 1);
	iota(fa.begin(),fa.end(),0);
	
	siz.resize(n + 1);
	fill(siz.begin(),siz.end(),1);
	
	son.resize(n + 1);
	for (int i = 1; i <= n; i++)
		son[i] = {i};
	
	ex.resize(n + 1);
	fill(ex.begin(),ex.end(),0);
}

int FIND(int x) {
	if (fa[x] == x)
		return x;
	else 
		return fa[x] = FIND(fa[x]);
}
	
void merge(int u,int v) {
	auto fu = FIND(u),fv = FIND(v);
	
	if (fu == fv)
		return;
	if (siz[fu] < siz[fv])
		swap(fu,fv);
	for (auto i : son[fv]) {
		if (i != fv)
			ex[i] = ex[i] + ex[fv] - ex[fu];
		else 
			ex[i] = ex[i] - ex[fu];
	}
	fa[fv] = fu;
	siz[fu] += siz[fv];
	
	son[fu].insert(son[fu].end(),son[fv].begin(),son[fv].end());
}

void add(int x,int v) {
	auto fx = FIND(x);
	ex[fx] += v;
}

int main() {
	ios::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
	
	cin >> n >> m;
	init(n);
	string s;
	for (int i = 1; i <= m; i++) {
		cin >> s;
		if (s == "join") {
			int x,y;
			cin >> x >> y;
			merge(x,y);
		}
		else {
			if (s == "add") {
				int x,v;
				cin >> x >> v;
				add(x,v);
			}
			else {
				int x;
				cin >> x;
				auto fx = FIND(x);
				if (x == fx)
					cout << ex[x] << endl;
				else 
					cout << ex[x] + ex[fx] << endl;
			}
		}
	}
	return 0;
}

并查集代码WA on test7