Problem p02850 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef pair<ll, ll> P;
typedef pair<int, int> Pi;
typedef vector<ll> Vec;
typedef vector<int> Vi;
typedef vector<string> Vs;
typedef vector<vector<ll>> VV;
typedef vector<vector<int>> VVi;

#define REP(i, a, b) for (ll i = (a); i < (b); i++)
#define PER(i, a, b) for (ll i = (a); i >= (b); i--)
#define rep(i, n) REP(i, 0, n)
#define per(i, n) PER(i, n, 0)
const ll INF = 1e16 + 18;
const ll MAX = 100005;
const ll MOD = 1000000007;
#define Yes(n) cout << ((n) ? "Yes" : "No") << endl;
#define YES(n) cout << ((n) ? "YES" : "NO") << endl;
#define ALL(v) v.begin(), v.end()
#define pb(x) push_back(x)
#define mp(a, b) make_pair(a, b)
#define Each(a, b) for (auto &a : b)
#define REPM(i, mp) for (auto i = mp.begin(); i != mp.end(); ++i)
#define dbg(x_) cerr << #x_ << ":" << x_ << endl;
#define dbgmap(mp)                                                             \
  cerr << #mp << ":" << endl;                                                  \
  for (auto i = mp.begin(); i != mp.end(); ++i) {                              \
    cerr << i->first << ":" << i->second << endl;                              \
  }
#define dbgarr(n, m, arr)                                                      \
  rep(i, n) {                                                                  \
    rep(j, m) { cerr << arr[i][j] << " "; }                                    \
    cerr << endl;                                                              \
  }
#define dbgdp(n, arr)                                                          \
  rep(i, n) { cerr << arr[i] << " "; }                                         \
  cerr << endl;
#define sum(v) accumulate(ALL(v), 0)
#define fi first
#define se second

template <typename T1, typename T2>
ostream &operator<<(ostream &s, const pair<T1, T2> &p) {
  return s << "(" << p.first << ", " << p.second << ")";
}

// vector
template <typename T> ostream &operator<<(ostream &s, const vector<T> &v) {
  int len = v.size();
  for (int i = 0; i < len; ++i) {
    s << v[i];
    if (i < len - 1)
      s << "	";
  }
  return s;
}

// 2 dimentional vector
template <typename T>
ostream &operator<<(ostream &s, const vector<vector<T>> &vv) {
  int len = vv.size();
  for (int i = 0; i < len; ++i) {
    s << vv[i] << endl;
  }
  return s;
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << std::setprecision(10);

  ll n;
  cin >> n;

  VVi to(n);
  VVi color(n, Vi(n, 0));

  vector<Pi> edge;
  ll a, b;
  rep(i, n - 1) {
    cin >> a >> b;
    a--;
    b--;
    to[a].pb(b);
    to[b].pb(a);
    edge.emplace_back(a, b);
  }

  Vi par(n);
  stack<int> q;
  q.push(0);
  int k = 0;
  while (!q.empty()) {
    int now = q.top();
    q.pop();
    int c = 0;
    Each(nx, to[now]) {
      if (nx == par[now])
        continue;
      int &parc = color[now][par[now]];
      c++;
      if (c == parc) {
        c++;
      }
      par[nx] = now;
      color[now][nx] = c;
      color[nx][now] = c;
      q.push(nx);
      k = max(k, c);
    }
  }

  cout << k << endl;
  rep(i, n - 1) { cout << color[edge[i].fi][edge[i].se] << endl; }

  return 0;
}


Fixed submission:
#include <bits/stdc++.h>

using namespace std;

typedef long long ll;
typedef pair<ll, ll> P;
typedef pair<int, int> Pi;
typedef vector<ll> Vec;
typedef vector<int> Vi;
typedef vector<string> Vs;
typedef vector<vector<ll>> VV;
typedef vector<vector<int>> VVi;

#define REP(i, a, b) for (ll i = (a); i < (b); i++)
#define PER(i, a, b) for (ll i = (a); i >= (b); i--)
#define rep(i, n) REP(i, 0, n)
#define per(i, n) PER(i, n, 0)
const ll INF = 1e16 + 18;
const ll MAX = 100005;
const ll MOD = 1000000007;
#define Yes(n) cout << ((n) ? "Yes" : "No") << endl;
#define YES(n) cout << ((n) ? "YES" : "NO") << endl;
#define ALL(v) v.begin(), v.end()
#define pb(x) push_back(x)
#define mp(a, b) make_pair(a, b)
#define Each(a, b) for (auto &a : b)
#define REPM(i, mp) for (auto i = mp.begin(); i != mp.end(); ++i)
#define dbg(x_) cerr << #x_ << ":" << x_ << endl;
#define dbgmap(mp)                                                             \
  cerr << #mp << ":" << endl;                                                  \
  for (auto i = mp.begin(); i != mp.end(); ++i) {                              \
    cerr << i->first << ":" << i->second << endl;                              \
  }
#define dbgarr(n, m, arr)                                                      \
  rep(i, n) {                                                                  \
    rep(j, m) { cerr << arr[i][j] << " "; }                                    \
    cerr << endl;                                                              \
  }
#define dbgdp(n, arr)                                                          \
  rep(i, n) { cerr << arr[i] << " "; }                                         \
  cerr << endl;
#define sum(v) accumulate(ALL(v), 0)
#define fi first
#define se second

template <typename T1, typename T2>
ostream &operator<<(ostream &s, const pair<T1, T2> &p) {
  return s << "(" << p.first << ", " << p.second << ")";
}

// vector
template <typename T> ostream &operator<<(ostream &s, const vector<T> &v) {
  int len = v.size();
  for (int i = 0; i < len; ++i) {
    s << v[i];
    if (i < len - 1)
      s << "	";
  }
  return s;
}

// 2 dimentional vector
template <typename T>
ostream &operator<<(ostream &s, const vector<vector<T>> &vv) {
  int len = vv.size();
  for (int i = 0; i < len; ++i) {
    s << vv[i] << endl;
  }
  return s;
}

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cout << std::setprecision(10);

  ll n;
  cin >> n;

  VVi to(n);
  // VVi color(n,Vi(n,0));
  vector<map<int, int>> color(n);
  vector<Pi> edge;
  ll a, b;
  rep(i, n - 1) {
    cin >> a >> b;
    a--;
    b--;
    to[a].pb(b);
    to[b].pb(a);
    edge.emplace_back(a, b);
  }

  Vi par(n);
  stack<int> q;
  q.push(0);
  int k = 0;
  while (!q.empty()) {
    int now = q.top();
    q.pop();
    int c = 0;
    Each(nx, to[now]) {
      if (nx == par[now])
        continue;
      int &parc = color[now][par[now]];
      c++;
      if (c == parc) {
        c++;
      }
      par[nx] = now;
      color[now][nx] = c;
      color[nx][now] = c;
      q.push(nx);
      k = max(k, c);
    }
  }

  cout << k << endl;
  rep(i, n - 1) { cout << color[edge[i].fi][edge[i].se] << endl; }

  return 0;
}