Problem p02749 (C++)

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

#define li long long int
#define rep(i, to) for (li i = 0; i < ((li)(to)); i++)
#define repp(i, start, to) for (li i = (li)(start); i < ((li)(to)); i++)
#define pb push_back
#define sz(v) ((li)(v).size())
#define bgn(v) ((v).begin())
#define eend(v) ((v).end())
#define allof(v) (v).begin(), (v).end()
#define dodp(v, n) memset(v, (li)n, sizeof(v))
#define bit(n) (1ll << (li)(n))
#define mp(a, b) make_pair(a, b)
#define rin rep(i, n)
#define EPS 1e-12
#define ETOL 1e-8
#define MOD 998244353
typedef pair<li, li> PI;

#define INF bit(60)

#define DBGP 1

#define idp if (DBGP)
#define F first
#define S second
#define p2(a, b) idp cout << a << "\t" << b << endl
#define p3(a, b, c) idp cout << a << "\t" << b << "\t" << c << endl
#define p4(a, b, c, d)                                                         \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << endl
#define p5(a, b, c, d, e)                                                      \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << "\t" << e << endl
#define p6(a, b, c, d, e, f)                                                   \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << "\t" << e << "\t"    \
           << f << endl
#define p7(a, b, c, d, e, f, g)                                                \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << "\t" << e << "\t"    \
           << f << "\t" << g << endl
#define p8(a, b, c, d, e, f, g, h)                                             \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << "\t" << e << "\t"    \
           << f << "\t" << g << "\t" << h << endl
#define p9(a, b, c, d, e, f, g, h, i)                                          \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << "\t" << e << "\t"    \
           << f << "\t" << g << "\t" << h << "\t" << i << endl
#define p10(a, b, c, d, e, f, g, h, i, j)                                      \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << "\t" << e << "\t"    \
           << f << "\t" << g << "\t" << h << "\t" << i << "\t" << j << endl
#define foreach(it, v)                                                         \
  for (__typeof((v).begin()) it = (v).begin(); it != (v).end(); ++it)
#define p2p(x) idp p2((x).F, (x).S)
#define dump(x, n)                                                             \
  idp {                                                                        \
    rep(i, n) { cout << x[i] << " "; }                                         \
    puts("");                                                                  \
  }
#define dump2(x, n)                                                            \
  idp {                                                                        \
    rep(i, n) { cout << "[" << x[i].F << " , " << x[i].S << "] "; }            \
    puts("");                                                                  \
  }
#define dumpi(x)                                                               \
  idp {                                                                        \
    foreach (it, x) {                                                          \
      cout << (*it) << " ";                                                    \
    }                                                                          \
    puts("");                                                                  \
  }
#define dumpi2(x)                                                              \
  idp {                                                                        \
    foreach (it, x) {                                                          \
      cout << "[" << (it)->F << " , " << (it)->S << "] ";                      \
    }                                                                          \
    puts("");                                                                  \
  }

#define read2d(a, w, h) rep(i, h) rep(j, w) cin >> a[i][j]
#define dump2d(a, w, h)                                                        \
  rep(i, h) {                                                                  \
    rep(j, w) cout << a[i][j] << " ";                                          \
    puts("");                                                                  \
  }

typedef pair<li, li> PI;

li d[200100];

li n;
vector<li> edges[200200];

li res[200200];

int main() {
  li n;
  cin >> n;
  rep(i, n - 1) {
    li a, b;
    cin >> a >> b;
    a--;
    b--;
    edges[a].pb(b);
    edges[b].pb(a);
  }

  rin { d[i] = INF; }

  stack<PI> stk;
  stk.push({0, 0});
  while (!stk.empty()) {
    li now = stk.top().F;
    li distance = stk.top().S;
    stk.pop();
    if (d[now] != INF) {
      continue;
    }
    d[now] = distance;
    for (auto &&next : edges[now]) {
      if (d[next] != INF) {
        continue;
      }
      stk.emplace(next, (distance + 1) % 2);
    }
  }

  li cnt[2];
  rin { cnt[d[i]]++; }
  if (cnt[0] * 3 < n) {
    queue<li> q12;
    queue<li> q3;
    rin {
      if ((i + 1) % 3 == 0) {
        q3.push(i + 1);
      } else {
        q12.push(i + 1);
      }
    }
    rin {
      if (d[i] == 0) {
        res[i] = q3.front();
        q3.pop();
      } else {
        if (!q12.empty()) {
          res[i] = q12.front();
          q12.pop();
        } else {
          res[i] = q3.front();
          q3.pop();
        }
      }
    }
  } else if (cnt[1] * 3 < n) {
    queue<li> q12;
    queue<li> q3;
    rin {
      if ((i + 1) % 3 == 0) {
        q3.push(i + 1);
      } else {
        q12.push(i + 1);
      }
    }
    rin {
      if (d[i] == 1) {
        res[i] = q3.front();
        q3.pop();
      } else {
        if (!q12.empty()) {
          res[i] = q12.front();
          q12.pop();
        } else {
          res[i] = q3.front();
          q3.pop();
        }
      }
    }
  } else {
    queue<li> q[3];
    rin { q[(i + 1) % 3].push(i + 1); }
    rin {
      if (d[i] == 0) {
        if (q[1].empty()) {
          res[i] = q[0].front();
          q[0].pop();
        } else {
          res[i] = q[1].front();
          q[1].pop();
        }
      } else {
        if (q[2].empty()) {
          res[i] = q[0].front();
          q[0].pop();
        } else {
          res[i] = q[2].front();
          q[2].pop();
        }
      }
    }
  }
  rin { cout << res[i] << " "; }
  cout << endl;

  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
using namespace std;

#define li long long int
#define rep(i, to) for (li i = 0; i < ((li)(to)); i++)
#define repp(i, start, to) for (li i = (li)(start); i < ((li)(to)); i++)
#define pb push_back
#define sz(v) ((li)(v).size())
#define bgn(v) ((v).begin())
#define eend(v) ((v).end())
#define allof(v) (v).begin(), (v).end()
#define dodp(v, n) memset(v, (li)n, sizeof(v))
#define bit(n) (1ll << (li)(n))
#define mp(a, b) make_pair(a, b)
#define rin rep(i, n)
#define EPS 1e-12
#define ETOL 1e-8
#define MOD 998244353
typedef pair<li, li> PI;

#define INF bit(60)

#define DBGP 1

#define idp if (DBGP)
#define F first
#define S second
#define p2(a, b) idp cout << a << "\t" << b << endl
#define p3(a, b, c) idp cout << a << "\t" << b << "\t" << c << endl
#define p4(a, b, c, d)                                                         \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << endl
#define p5(a, b, c, d, e)                                                      \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << "\t" << e << endl
#define p6(a, b, c, d, e, f)                                                   \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << "\t" << e << "\t"    \
           << f << endl
#define p7(a, b, c, d, e, f, g)                                                \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << "\t" << e << "\t"    \
           << f << "\t" << g << endl
#define p8(a, b, c, d, e, f, g, h)                                             \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << "\t" << e << "\t"    \
           << f << "\t" << g << "\t" << h << endl
#define p9(a, b, c, d, e, f, g, h, i)                                          \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << "\t" << e << "\t"    \
           << f << "\t" << g << "\t" << h << "\t" << i << endl
#define p10(a, b, c, d, e, f, g, h, i, j)                                      \
  idp cout << a << "\t" << b << "\t" << c << "\t" << d << "\t" << e << "\t"    \
           << f << "\t" << g << "\t" << h << "\t" << i << "\t" << j << endl
#define foreach(it, v)                                                         \
  for (__typeof((v).begin()) it = (v).begin(); it != (v).end(); ++it)
#define p2p(x) idp p2((x).F, (x).S)
#define dump(x, n)                                                             \
  idp {                                                                        \
    rep(i, n) { cout << x[i] << " "; }                                         \
    puts("");                                                                  \
  }
#define dump2(x, n)                                                            \
  idp {                                                                        \
    rep(i, n) { cout << "[" << x[i].F << " , " << x[i].S << "] "; }            \
    puts("");                                                                  \
  }
#define dumpi(x)                                                               \
  idp {                                                                        \
    foreach (it, x) {                                                          \
      cout << (*it) << " ";                                                    \
    }                                                                          \
    puts("");                                                                  \
  }
#define dumpi2(x)                                                              \
  idp {                                                                        \
    foreach (it, x) {                                                          \
      cout << "[" << (it)->F << " , " << (it)->S << "] ";                      \
    }                                                                          \
    puts("");                                                                  \
  }

#define read2d(a, w, h) rep(i, h) rep(j, w) cin >> a[i][j]
#define dump2d(a, w, h)                                                        \
  rep(i, h) {                                                                  \
    rep(j, w) cout << a[i][j] << " ";                                          \
    puts("");                                                                  \
  }

typedef pair<li, li> PI;

li d[200100];

li n;
vector<li> edges[200200];

li res[200200];

int main() {
  li n;
  cin >> n;
  rep(i, n - 1) {
    li a, b;
    cin >> a >> b;
    a--;
    b--;
    edges[a].pb(b);
    edges[b].pb(a);
  }

  rin { d[i] = INF; }

  stack<PI> stk;
  stk.push({0, 0});
  while (!stk.empty()) {
    li now = stk.top().F;
    li distance = stk.top().S;
    stk.pop();
    if (d[now] != INF) {
      continue;
    }
    d[now] = distance;
    for (auto &&next : edges[now]) {
      if (d[next] != INF) {
        continue;
      }
      stk.emplace(next, (distance + 1) % 2);
    }
  }

  li cnt[2] = {0};
  rin { cnt[d[i]]++; }
  if (cnt[0] * 3 < n) {
    queue<li> q12;
    queue<li> q3;
    rin {
      if ((i + 1) % 3 == 0) {
        q3.push(i + 1);
      } else {
        q12.push(i + 1);
      }
    }
    rin {
      if (d[i] == 0) {
        res[i] = q3.front();
        q3.pop();
      } else {
        if (!q12.empty()) {
          res[i] = q12.front();
          q12.pop();
        } else {
          res[i] = q3.front();
          q3.pop();
        }
      }
    }
  } else if (cnt[1] * 3 < n) {
    queue<li> q12;
    queue<li> q3;
    rin {
      if ((i + 1) % 3 == 0) {
        q3.push(i + 1);
      } else {
        q12.push(i + 1);
      }
    }
    rin {
      if (d[i] == 1) {
        res[i] = q3.front();
        q3.pop();
      } else {
        if (!q12.empty()) {
          res[i] = q12.front();
          q12.pop();
        } else {
          res[i] = q3.front();
          q3.pop();
        }
      }
    }
  } else {
    queue<li> q[3];
    rin { q[(i + 1) % 3].push(i + 1); }
    rin {
      if (d[i] == 0) {
        if (q[1].empty()) {
          res[i] = q[0].front();
          q[0].pop();
        } else {
          res[i] = q[1].front();
          q[1].pop();
        }
      } else {
        if (q[2].empty()) {
          res[i] = q[0].front();
          q[0].pop();
        } else {
          res[i] = q[2].front();
          q[2].pop();
        }
      }
    }
  }
  rin { cout << res[i] << " "; }
  cout << endl;

  return 0;
}