Language: C++

#include <vector> 
#include <list> 
#include <map>
#include <set>//2分探索木
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>
#include <queue>// キュー　優先度付きキュー
#include <stack>
#include <complex>
#include <memory>
#include <assert.h>
#ifdef LOCAL
#include "UnionFind.h"//同じグループに属するか
#include "Prime.h"//素数判定
#include "RMQ.h"//区間最小値
#include "BIT.h"//累積和
#include "Dijkstra.h"//単一始点最短経路(負の辺があるときは動作しない)　O(ElogV)
#include "Kruskal.h"//最小全域木 O(ElogV)
#include "Factorial.h"//階乗　組み合わせ　 
#endif

using namespace std;

//conversion
//------------------------------------------
inline long long toInt(string s) { long long v; istringstream sin(s); sin >> v; return v; }
template<class T> inline string toString(T x) { ostringstream sout; sout << x; return sout.str(); }



//math
//-------------------------------------------
template<class T> inline T sqr(T x) { return x * x; }

//typedef
//------------------------------------------
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<string> vs;
typedef pair<int, int> pii;
typedef long long ll;
typedef vector<ll> vll;
typedef vector<pii> vpii;

//container util
//------------------------------------------
#define all(a)  (a).begin(),(a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define pb push_back
#define mp make_pair
#define sz(a) int((a).size())
#define each(t,c) for(typeof((c).begin()) t=(c).begin(); t!=(c).end(); ++t)
#define exist(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())


//文字列分割
std::vector<std::string> split(std::string str, set<char> del) {
	std::vector<std::string> result; std::string subStr;
	for (const char c : str) {
		if (exist(del, c)) { result.push_back(subStr); subStr.clear(); }
		else { subStr += c; }
	}
	result.push_back(subStr);
	return result;
}


//repetition
//------------------------------------------
#define FOR(t,a,b) for(int t=(a);t<(b);++t)
#define rep(t,n)  FOR(t,0,n)

//constant
//------------------------------------------
const double EPS = 1e-10;
const double PI = acos(-1.0);

//clear memory
//------------------------------------------
#define clr(a) memset((a), 0 ,sizeof(a))

//debug
//------------------------------------------
#if defined(__GNUC__) 
#include <assert.h>
#define ASSERT_(x) assert(x)
#else
#include <assert.h>
#define ASSERT_(x) assert(x)
#endif
#ifdef _DEBUG
#define dump(x)  cerr << #x << '=' << (x) << endl;
#define debug(x) cerr << #x << '=' << (x) << '('<<'L' << __LINE__ << ')' << ' ' << __FILE__ << endl;
#define ASSERT(x) {if (!(x)){std::cerr << "\nError!!\n" << "info string file:" << __FILE__ << " line:" << __LINE__ <<" "<< #x<< std::endl;ASSERT_(x);}}
#else
#define ASSERT(x) ((void)0)
#define debug(x) ((void)0)
#define dump(x)  ((void)0)
#endif // _DEBUG

//vector
template<class T> void showVector(vector<T>& v) {
	for (int i = 0; i < v.size(); ++i)
		cerr << v[i] << " ";
	cerr << endl;
}

// 多次元 vector 生成
template<class T>
vector<T> make_vec(size_t a) {
	return vector<T>(a);
}
template<class T, class... Ts>
auto make_vec(size_t a, Ts... ts) {
	return vector<decltype(make_vec<T>(ts...))>(a, make_vec<T>(ts...));
}

//mod
//-------------------------------------------
const ll mod = 1000000007;
ll mod_pow(ll x, ll n, ll mod) {
	if (n == 0) { return 1; }
	ll res = mod_pow(x * x % mod, n / 2, mod);
	if (n & 1) { res = res * x % mod; }
	return res;
}

//組み合わせ数
ll conbination(ll n, ll r) {
	if (r > n || r < 0LL) { return 0LL; }
	ll i;
	ll s = 1LL;
	for (i = 1LL; i <= r; i++) { s = s * (n + 1LL - i) / i; }
	return s;
}


//bitop
//-------------------------------------------
#if defined(__GNUC__)
#include <immintrin.h>
int popcount(int a) {
	return __builtin_popcount(a);
}
#elif defined(_MSC_VER)
#include <intrin.h>
int popcount(int a) {
	return __popcnt(a);
}
#endif 

//gcd lcm
//-------------------------------------------
ll gcd(ll a, ll b) { if (a % b == 0) { return b; } else return gcd(b, a % b); }
ll lcm(ll a, ll b) { return a / gcd(a, b) * b; }


//YES_NO
//------------------------------------------
#define Yes_ cout<<"Yes"<<endl; return 0;
#define No_ cout<<"No"<<endl; return 0;

#define YES_ cout<<"YES"<<endl; return 0;
#define NO_ cout<<"NO"<<endl; return 0;

#define POSSIBLE cout<<"POSSIBLE"<<endl; return 0;
#define IMPOSSIBLE cout<<"IMPOSSIBLE"<<endl; return 0;

//matrix
//------------------------------------------
template <class T> class matrix : public vector< vector<T> > {
private:
	int tate_, yoko_;
public:
	matrix(const int tate__, const int yoko__) {
		ASSERT(tate__ > 0); ASSERT(yoko__ > 0);
		this->resize(tate__); for (size_t i = 0; i < this->size(); i++) { (*this)[i].resize(yoko__); }tate_ = tate__; yoko_ = yoko__;
	}
	matrix() {};
	int tate() const { return tate_; } int yoko() const { return yoko_; }
	void resizematrix(const int tate__, const int yoko__) {
		ASSERT(tate__ > 0); ASSERT(yoko__ > 0);
		this->resize(tate__); for (size_t i = 0; i < this->size(); i++) { (*this)[i].resize(yoko__); }tate_ = tate__; yoko_ = yoko__;
	}
	void setzero() { for (int i = 0; i < tate(); i++) for (int j = 0; j < yoko(); j++) { (*this)[i][j] = 0; } }
};

template<class T> std::ostream& operator<<(std::ostream & os, const matrix<T> & m)
{
	for (int j = 0; j < m.tate(); j++) { for (int i = 0; i < m.yoko(); i++) { os << (int)m[j][i]; }os << endl; }
	return os;
}
#if 1
//time
//------------------------------------------
#if defined(__GNUC__) 
#include <sys/time.h>
#include <immintrin.h>
#include <string.h>
ll starttime;
inline ll now() {
	struct timeval tv;
	gettimeofday(&tv, NULL);
	ll t = tv.tv_sec * 1000LL + tv.tv_usec / 1000LL;
	return t;
}
inline ll elapsed() { return now() - starttime; }
#else
#include <chrono>
#include <intrin.h>
typedef std::chrono::milliseconds::rep TimePoint;
inline TimePoint now() { return std::chrono::duration_cast<std::chrono::milliseconds>(std::chrono::steady_clock::now().time_since_epoch()).count(); }
TimePoint starttime;
inline TimePoint elapsed() { return now() - starttime; }
#endif
#endif

//=====================================================
//http://drken1215.hatenablog.com/entry/2019/03/03/224600
/*
どの島とどの島がつながっているか UnionFind

辺を取り除いてゆくのは何もない状態から辺を足してゆくと考えるのがよい

i番目の辺(a,b)を追加する
	a,bが同じグループなら何も起こらない

	違うグループの場合
	a側のgroup sizeがSA
	b側のgroup sizeがSB
	とすると
	n*(n-1)/2からSA*SBを引いてゆく
*/
int main() {
	
	ll n, m;
	cin >> n >> m;
	vll a(m), b(m);
	rep(i, m) {
		cin >> a[i] >> b[i]; a[i]--; b[i]--;
	}

	UnionFind uf(n);

	ll ans = (n - 1) * n / 2;
	vll ANSs;
	for (int i = m - 1; i >= 0; i--) {
		ANSs.push_back(ans);

		ll k = a[i], l = b[i];
		if (uf.same(k, l)) { continue; }
		ll sa = uf.size(k), sb = uf.size(l);

		uf.unite(k, l);

		ans -= sa * sb;

	}
	reverse(all(ANSs));
	rep(i, sz(ANSs)) {
		cout << ANSs[i] << endl;
	}

}


Compiler output:
a.cc: In function 'int main()':
a.cc:259:9: error: 'UnionFind' was not declared in this scope
  259 |         UnionFind uf(n);
      |         ^~~~~~~~~
a.cc:267:21: error: 'uf' was not declared in this scope
  267 |                 if (uf.same(k, l)) { continue; }
      |                     ^~
a.cc:268:25: error: 'uf' was not declared in this scope
  268 |                 ll sa = uf.size(k), sb = uf.size(l);
      |                         ^~
a.cc:272:29: error: 'sb' was not declared in this scope; did you mean 'sa'?
  272 |                 ans -= sa * sb;
      |                             ^~
      |                             sa