Problem p03108 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <cassert>
#include <cmath>
#include <cstdio>
#include <fstream>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <string>
#include <vector>
using namespace std;

#define REP(i, m, n) for (int i = (m); i < (int)(n); i++)
#define RREP(i, m, n) for (int i = (int)(n - 1); i >= m; i--)
#define rep(i, n) REP(i, 0, n)
#define rrep(i, n) RREP(i, 0, n)
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define aut(r, v) __typeof(v) r = (v)
#define each(it, o) for (aut(it, (o).begin()); it != (o).end(); ++it)
#define reach(it, o) for (aut(it, (o).rbegin()); it != (o).rend(); ++it)
#define fi first
#define se second
#define debug(...)                                                             \
  {                                                                            \
    cerr << "[L" << __LINE__ << "] ";                                          \
    _debug(__VA_ARGS__);                                                       \
  }

template <typename T1, typename T2>
ostream &operator<<(ostream &o, const pair<T1, T2> &p) {
  return o << "(" << p.first << ", " << p.second << ")";
}
template <typename T> string join(const vector<T> &v, string del = ", ") {
  stringstream s;
  rep(i, v.size()) s << del << v[i];
  return s.str().substr(del.size());
}
template <typename T> ostream &operator<<(ostream &o, const vector<T> &v) {
  if (v.size())
    o << "[" << join(v) << "]";
  return o;
}
template <typename T>
ostream &operator<<(ostream &o, const vector<vector<T>> &vv) {
  int l = vv.size();
  if (l) {
    o << endl;
    rep(i, l) {
      o << (i == 0 ? "[ " : ",\n  ") << vv[i] << (i == l - 1 ? " ]" : "");
    }
  }
  return o;
}
template <typename T> ostream &operator<<(ostream &o, const set<T> &st) {
  vector<T> v(st.begin(), st.end());
  o << "{ " << join(v) << " }";
  return o;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &o, const map<T1, T2> &m) {
  each(p, m) {
    o << (p == m.begin() ? "{ " : ",\n  ") << *p
      << (p == --m.end() ? " }" : "");
  }
  return o;
}
inline void _debug() { cerr << endl; }
template <class First, class... Rest>
void _debug(const First &first, const Rest &...rest) {
  cerr << first << " ";
  _debug(rest...);
}

typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vl;
typedef vector<vl> vvl;

const double PI = (1 * acos(0.0));
const double INF = 0x3f3f3f3f;
const double INFL = 0x3f3f3f3f3f3f3f3fLL;
const double EPS = 1e-9;
const double mod = 1e9 + 7;

inline void finput(string filename) { freopen(filename.c_str(), "r", stdin); }

struct UnionFind {
  vector<int> dat;
  UnionFind(int _size) : dat(_size, -1) {}
  bool unionSet(int x, int y) {
    x = root(x);
    y = root(y);
    if (x != y) {
      if (dat[y] < dat[x])
        swap(x, y);
      dat[x] += dat[y];
      dat[y] = x;
    }
    return x != y;
  }
  bool findSet(int x, int y) { return root(x) == root(y); }
  int root(int x) { return dat[x] < 0 ? x : dat[x] = root(dat[x]); }
  int size(int x) { return -dat[root(x)]; }
};

int a[10005], b[10005];
int n, m;

int main() {
  ios_base::sync_with_stdio(0);
  // finput("./input");

  cin >> n >> m;
  rep(i, m) {
    cin >> a[i] >> b[i];
    a[i]--;
    b[i]--;
  }

  vl answers;
  ll ans = n * (ll)(n - 1) / 2;
  UnionFind uf = UnionFind(n);
  rrep(i, m) {
    answers.push_back(ans);
    if (uf.findSet(a[i], b[i]))
      continue;
    ans -= uf.size(a[i]) * (ll)uf.size(b[i]);
    uf.unionSet(a[i], b[i]);
  }
  rrep(i, m) cout << answers[i] << endl;
  return 0;
}


Fixed submission:
#include <algorithm>
#include <cassert>
#include <cmath>
#include <cstdio>
#include <fstream>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <sstream>
#include <string>
#include <vector>
using namespace std;

#define REP(i, m, n) for (int i = (m); i < (int)(n); i++)
#define RREP(i, m, n) for (int i = (int)(n - 1); i >= m; i--)
#define rep(i, n) REP(i, 0, n)
#define rrep(i, n) RREP(i, 0, n)
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define aut(r, v) __typeof(v) r = (v)
#define each(it, o) for (aut(it, (o).begin()); it != (o).end(); ++it)
#define reach(it, o) for (aut(it, (o).rbegin()); it != (o).rend(); ++it)
#define fi first
#define se second
#define debug(...)                                                             \
  {                                                                            \
    cerr << "[L" << __LINE__ << "] ";                                          \
    _debug(__VA_ARGS__);                                                       \
  }

template <typename T1, typename T2>
ostream &operator<<(ostream &o, const pair<T1, T2> &p) {
  return o << "(" << p.first << ", " << p.second << ")";
}
template <typename T> string join(const vector<T> &v, string del = ", ") {
  stringstream s;
  rep(i, v.size()) s << del << v[i];
  return s.str().substr(del.size());
}
template <typename T> ostream &operator<<(ostream &o, const vector<T> &v) {
  if (v.size())
    o << "[" << join(v) << "]";
  return o;
}
template <typename T>
ostream &operator<<(ostream &o, const vector<vector<T>> &vv) {
  int l = vv.size();
  if (l) {
    o << endl;
    rep(i, l) {
      o << (i == 0 ? "[ " : ",\n  ") << vv[i] << (i == l - 1 ? " ]" : "");
    }
  }
  return o;
}
template <typename T> ostream &operator<<(ostream &o, const set<T> &st) {
  vector<T> v(st.begin(), st.end());
  o << "{ " << join(v) << " }";
  return o;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &o, const map<T1, T2> &m) {
  each(p, m) {
    o << (p == m.begin() ? "{ " : ",\n  ") << *p
      << (p == --m.end() ? " }" : "");
  }
  return o;
}
inline void _debug() { cerr << endl; }
template <class First, class... Rest>
void _debug(const First &first, const Rest &...rest) {
  cerr << first << " ";
  _debug(rest...);
}

typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vl;
typedef vector<vl> vvl;

const double PI = (1 * acos(0.0));
const double INF = 0x3f3f3f3f;
const double INFL = 0x3f3f3f3f3f3f3f3fLL;
const double EPS = 1e-9;
const double mod = 1e9 + 7;

inline void finput(string filename) { freopen(filename.c_str(), "r", stdin); }

struct UnionFind {
  vector<int> dat;
  UnionFind(int _size) : dat(_size, -1) {}
  bool unionSet(int x, int y) {
    x = root(x);
    y = root(y);
    if (x != y) {
      if (dat[y] < dat[x])
        swap(x, y);
      dat[x] += dat[y];
      dat[y] = x;
    }
    return x != y;
  }
  bool findSet(int x, int y) { return root(x) == root(y); }
  int root(int x) { return dat[x] < 0 ? x : dat[x] = root(dat[x]); }
  int size(int x) { return -dat[root(x)]; }
};

int a[100005], b[100005];
int n, m;

int main() {
  ios_base::sync_with_stdio(0);
  // finput("./input");

  cin >> n >> m;
  rep(i, m) {
    cin >> a[i] >> b[i];
    a[i]--;
    b[i]--;
  }

  vl answers;
  ll ans = n * (ll)(n - 1) / 2;
  UnionFind uf = UnionFind(n);
  rrep(i, m) {
    answers.push_back(ans);
    if (uf.findSet(a[i], b[i]))
      continue;
    ans -= uf.size(a[i]) * (ll)uf.size(b[i]);
    uf.unionSet(a[i], b[i]);
  }
  rrep(i, m) cout << answers[i] << endl;
  return 0;
}