这份代码在洛谷能通过，在AcWing上不能：

#include<bits/stdc++.h>
using namespace std;
const int N = 30009;
int t;
int fa[N];
int siz[N],dis[N];
int father(int x){
	if(x == fa[x])
		return x;
	int root = father(fa[x]);
	dis[x] += dis[fa[x]];
	return fa[x] = root;
}
void join(int x,int y){
	int fa_x = father(x),fa_y = father(y);
	fa[fa_x] = fa_y;
	dis[fa_x] = siz[fa_y];
	siz[fa_y] += siz[fa_x];
}
int query(int x,int y){
	int fa_x = father(x),fa_y = father(y);
	if(fa_x == fa_y)
		return abs(dis[x] - dis[y]) - 1;
	return -1;
}
int main(){
	ios::sync_with_stdio(false);
	cin.tie(0);cout.tie(0);
	cin >> t;
	for(int i = 1;i < N;i++){
		fa[i] = i;
		siz[i] = 1;
	}
	while(t--){
		string op;
		int i,j;
		cin >> op >> i >> j;
		if(op == "M")
			join(i,j);
		else
			cout << query(i,j) << '\n';
	}
	return 0;
}

hack：

in：

4
M 2 3
C 1 2
M 2 4
C 4 4

out：

-1
0