Problem p03142 (C++)

Buggy submission (status: Time Limit Exceeded):
// #include <bits/stdc++.h>

#include <algorithm>
#include <iostream>

#include <array>
#include <bitset>
#include <complex>
#include <cstring>
#include <deque>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <valarray>
#include <vector>

#include <cassert>
#include <chrono>
#include <cmath>
#include <functional>
#include <iomanip>
#include <numeric>
#include <random>

using namespace std;
// #define int long long

typedef long long ll;
typedef unsigned long long ull;
// typedef unsigned __int128 HASH;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<ull, ull> pullull;
typedef pair<ll, int> plli;
typedef pair<double, int> pdi;
typedef pair<long double, int> pdbi;
typedef pair<int, pii> pipii;
typedef pair<ll, pll> plpll;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef vector<pii> vpii;
typedef vector<vector<int>> mat;

#define rep(i, n) for (int i = 0; i < (n); i++)
#define rep2(i, a, b) for (int i = (a); i < (b); i++)
#define rrep(i, n) for (int i = (n); i > 0; i--)
#define rrep2(i, a, b) for (int i = (a); i > b; i--)
#define pb push_back
#define fi first
#define se second
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()

const ll hmod1 = 999999937;
const ll hmod2 = 1000000000 + 9;
const int INF = 1 << 30;
const ll INFLL = 1LL << 62;
const long double EPS = 1e-12;
const ll mod = 1000000000 + 7;
// const ll mod = 998244353;
const int dx4[4] = {1, 0, -1, 0};
const int dy4[4] = {0, 1, 0, -1};
const int dx8[8] = {1, 1, 1, 0, 0, -1, -1, -1};
const int dy8[8] = {0, 1, -1, 1, -1, 0, 1, -1};
const long double pi = 3.141592653589793;

#define addm(X, Y) (X) = ((X) + ((Y) % mod) + mod) % mod
#define inside(y, x, h, w)                                                     \
  (0 <= (y) && (y) < (h) && 0 <= (x) && (x) < (w)) ? true : false

// debug
#define DEBUG

#define DUMPOUT cout

#ifdef DEBUG
#define dump(...)                                                              \
  DUMPOUT << #__VA_ARGS__ << " :[" << __FUNCTION__ << ":" << __LINE__ << "]"   \
          << endl;                                                             \
  DUMPOUT << "    ";                                                           \
  dump_func(__VA_ARGS__)
#else
#define dump(...)
#endif

void dump_func() { DUMPOUT << endl; };

template <class Head, class... Tail>
void dump_func(Head &&head, Tail &&...tail) {
  DUMPOUT << head;
  if (sizeof...(Tail) == 0)
    DUMPOUT << " ";
  else
    DUMPOUT << ", ";
  dump_func(std::move(tail)...);
}

// ostream
template <typename T> ostream &operator<<(ostream &os, vector<T> &vec) {
  os << "[";
  for (int i = 0; i < vec.size(); i++)
    os << vec[i] << (i + 1 == vec.size() ? "" : ", ");
  os << "]";
  return os;
}

template <typename T, typename U>
ostream &operator<<(ostream &os, pair<T, U> &pair_var) {
  os << "(" << pair_var.first << ", " << pair_var.second << ")";
  return os;
}

template <typename T, typename U>
ostream &operator<<(ostream &os, map<T, U> &map_var) {
  os << "[";
  for (auto itr = map_var.begin(); itr != map_var.end(); itr++) {
    os << "(" << itr->first << ", " << itr->second << ")";
    itr++;
    if (itr != map_var.end())
      os << ", ";
    itr--;
  }
  os << "]";
  return os;
}

template <typename T> ostream &operator<<(ostream &os, set<T> &set_var) {
  os << "[";
  for (auto itr = set_var.begin(); itr != set_var.end(); itr++) {
    os << *itr;
    ++itr;
    if (itr != set_var.end())
      os << ", ";
    itr--;
  }
  os << "]";
  return os;
}

int n, m;
int a[100000 + 5], b[100000 + 5];
vector<vector<int>> g(100000 + 5);
vector<int> ans(100000 + 5, -1);
vector<int> indeg(100000 + 5), outdeg(100000 + 5);
vector<bool> visited(100000 + 5);

void dfs(int now, int par) {
  visited[now] = true;
  if (par != -1 && ans[now] == -1) {
    ans[now] = par + 1;
  }
  for (auto nx : g[now]) {
    if (nx == par || visited[nx])
      continue;
    if (indeg[nx] == 1) {
      for (auto nx2 : g[now]) {
        indeg[nx2]--;
      }
      dfs(nx, now);
      for (auto nx2 : g[now]) {
        indeg[nx2]++;
      }
    }
  }
  return;
}

void bfs(int r, int par) {
  queue<pii> q;
  q.push({r, par});
  while (!q.empty()) {
    pii p = q.front();
    q.pop();
    int now = p.fi;
    int pa = p.se;
    visited[now] = true;
    if (now != r)
      ans[now] = pa + 1;
    for (auto nx : g[now]) {
      if (indeg[nx] == 1 && !visited[nx]) {
        visited[nx] = true;
        q.push({nx, now});
      }
    }
    for (auto nx : g[now]) {
      indeg[nx]--;
    }
  }
}

signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cin >> n >> m;
  rep(i, n - 1 + m) {
    cin >> a[i] >> b[i];
    a[i]--;
    b[i]--;
    indeg[b[i]]++;
    outdeg[a[i]]++;
    g[a[i]].push_back(b[i]);
  }
  int root = 0;
  rep(i, n) {
    if (indeg[i] == 0) {
      root = i;
      break;
    }
  }
  ans[root] = 0;
  dfs(root, -1);
  rep(i, n) { cout << ans[i] << endl; }
}


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

#include <algorithm>
#include <iostream>

#include <array>
#include <bitset>
#include <complex>
#include <cstring>
#include <deque>
#include <map>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <valarray>
#include <vector>

#include <cassert>
#include <chrono>
#include <cmath>
#include <functional>
#include <iomanip>
#include <numeric>
#include <random>

using namespace std;
// #define int long long

typedef long long ll;
typedef unsigned long long ull;
// typedef unsigned __int128 HASH;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<ull, ull> pullull;
typedef pair<ll, int> plli;
typedef pair<double, int> pdi;
typedef pair<long double, int> pdbi;
typedef pair<int, pii> pipii;
typedef pair<ll, pll> plpll;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef vector<pii> vpii;
typedef vector<vector<int>> mat;

#define rep(i, n) for (int i = 0; i < (n); i++)
#define rep2(i, a, b) for (int i = (a); i < (b); i++)
#define rrep(i, n) for (int i = (n); i > 0; i--)
#define rrep2(i, a, b) for (int i = (a); i > b; i--)
#define pb push_back
#define fi first
#define se second
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()

const ll hmod1 = 999999937;
const ll hmod2 = 1000000000 + 9;
const int INF = 1 << 30;
const ll INFLL = 1LL << 62;
const long double EPS = 1e-12;
const ll mod = 1000000000 + 7;
// const ll mod = 998244353;
const int dx4[4] = {1, 0, -1, 0};
const int dy4[4] = {0, 1, 0, -1};
const int dx8[8] = {1, 1, 1, 0, 0, -1, -1, -1};
const int dy8[8] = {0, 1, -1, 1, -1, 0, 1, -1};
const long double pi = 3.141592653589793;

#define addm(X, Y) (X) = ((X) + ((Y) % mod) + mod) % mod
#define inside(y, x, h, w)                                                     \
  (0 <= (y) && (y) < (h) && 0 <= (x) && (x) < (w)) ? true : false

// debug
#define DEBUG

#define DUMPOUT cout

#ifdef DEBUG
#define dump(...)                                                              \
  DUMPOUT << #__VA_ARGS__ << " :[" << __FUNCTION__ << ":" << __LINE__ << "]"   \
          << endl;                                                             \
  DUMPOUT << "    ";                                                           \
  dump_func(__VA_ARGS__)
#else
#define dump(...)
#endif

void dump_func() { DUMPOUT << endl; };

template <class Head, class... Tail>
void dump_func(Head &&head, Tail &&...tail) {
  DUMPOUT << head;
  if (sizeof...(Tail) == 0)
    DUMPOUT << " ";
  else
    DUMPOUT << ", ";
  dump_func(std::move(tail)...);
}

// ostream
template <typename T> ostream &operator<<(ostream &os, vector<T> &vec) {
  os << "[";
  for (int i = 0; i < vec.size(); i++)
    os << vec[i] << (i + 1 == vec.size() ? "" : ", ");
  os << "]";
  return os;
}

template <typename T, typename U>
ostream &operator<<(ostream &os, pair<T, U> &pair_var) {
  os << "(" << pair_var.first << ", " << pair_var.second << ")";
  return os;
}

template <typename T, typename U>
ostream &operator<<(ostream &os, map<T, U> &map_var) {
  os << "[";
  for (auto itr = map_var.begin(); itr != map_var.end(); itr++) {
    os << "(" << itr->first << ", " << itr->second << ")";
    itr++;
    if (itr != map_var.end())
      os << ", ";
    itr--;
  }
  os << "]";
  return os;
}

template <typename T> ostream &operator<<(ostream &os, set<T> &set_var) {
  os << "[";
  for (auto itr = set_var.begin(); itr != set_var.end(); itr++) {
    os << *itr;
    ++itr;
    if (itr != set_var.end())
      os << ", ";
    itr--;
  }
  os << "]";
  return os;
}

int n, m;
int a[100000 + 5], b[100000 + 5];
vector<vector<int>> g(100000 + 5);
vector<int> ans(100000 + 5, -1);
vector<int> indeg(100000 + 5), outdeg(100000 + 5);
vector<bool> visited(100000 + 5);

void dfs(int now, int par) {
  visited[now] = true;
  if (par != -1 && ans[now] == -1) {
    ans[now] = par + 1;
  }
  for (auto nx : g[now]) {
    if (nx == par || visited[nx])
      continue;
    if (indeg[nx] == 1) {
      for (auto nx2 : g[now]) {
        indeg[nx2]--;
      }
      dfs(nx, now);
      for (auto nx2 : g[now]) {
        indeg[nx2]++;
      }
    }
  }
  return;
}

void bfs(int r, int par) {
  queue<pii> q;
  q.push({r, par});
  while (!q.empty()) {
    pii p = q.front();
    q.pop();
    int now = p.fi;
    int pa = p.se;
    visited[now] = true;
    if (now != r)
      ans[now] = pa + 1;
    for (auto nx : g[now]) {
      if (indeg[nx] == 1 && !visited[nx]) {
        visited[nx] = true;
        q.push({nx, now});
      }
    }
    for (auto nx : g[now]) {
      indeg[nx]--;
    }
  }
}

signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cin >> n >> m;
  rep(i, n - 1 + m) {
    cin >> a[i] >> b[i];
    a[i]--;
    b[i]--;
    indeg[b[i]]++;
    outdeg[a[i]]++;
    g[a[i]].push_back(b[i]);
  }
  int root = 0;
  rep(i, n) {
    if (indeg[i] == 0) {
      root = i;
      break;
    }
  }
  ans[root] = 0;
  bfs(root, -1);
  rep(i, n) { cout << ans[i] << endl; }
}