Problem p03656 (C++)

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

#define PB push_back
#define PF push_front
#define LB lower_bound
#define UB upper_bound
#define fr(x) freopen(x, "r", stdin)
#define fw(x) freopen(x, "w", stdout)
#define iout(x) printf("%d\n", x)
#define lout(x) printf("%lld\n", x)
#define REP(x, l, u) for (int x = (l); x <= (u); x++)
#define RREP(x, l, u) for (int x = (l); x >= (u); x--)
#define mst(x, a) memset(x, a, sizeof(x))
#define PII pair<int, int>
#define PLL pair<ll, ll>
#define MP make_pair
#define se second
#define fi first
#define dbg(x) cout << #x << " = " << (x) << endl;
#define sz(x) ((int)x.size())
#define cl(x) x.clear()

typedef long long ll;
typedef unsigned long long ull;
typedef double db;
typedef long double ld;
using namespace std;

const int maxn = 600010;
const int mod = 1e9 + 7;
const int MAX = 1000000010;
const double eps = 1e-6;
const double PI = acos(-1);

template <typename T> inline void read(T &x) {
  x = 0;
  T f = 1;
  char ch;
  do {
    ch = getchar();
    if (ch == '-')
      f = -1;
  } while (ch < '0' || ch > '9');
  do
    x = x * 10 + ch - '0', ch = getchar();
  while (ch <= '9' && ch >= '0');
  x *= f;
}

template <typename A, typename B> inline void read(A &x, B &y) {
  read(x);
  read(y);
}
template <typename A, typename B, typename C>
inline void read(A &x, B &y, C &z) {
  read(x);
  read(y);
  read(z);
}
template <typename A, typename B, typename C, typename D>
inline void read(A &x, B &y, C &z, D &w) {
  read(x);
  read(y);
  read(z);
  read(w);
}
template <typename A, typename B> inline A fexp(A x, B p) {
  A ans = 1;
  for (; p; p >>= 1, x = 1LL * x * x % mod)
    if (p & 1)
      ans = 1LL * ans * x % mod;
  return ans;
}
template <typename A, typename B> inline A fexp(A x, B p, A mo) {
  A ans = 1;
  for (; p; p >>= 1, x = 1LL * x * x % mo)
    if (p & 1)
      ans = 1LL * ans * x % mo;
  return ans;
}

int n, rt1, rt2;

int fa[maxn];

vector<int> G[maxn];

int f[maxn], Ans[maxn], S[maxn], top;

map<PII, int> mp;

void Euler(int u) {
  for (int i = (int)G[u].size() - 1; i >= 0; i--) {
    int v = G[u][i];
    G[u].pop_back();
    if (!mp[MP(u, v)]) {
      mp[MP(v, u)] = mp[MP(u, v)] = 1;
      Euler(v);
    }
  }
  S[++top] = u;
}

void dfs(int u) {
  f[u] = 1;
  for (auto v : G[u])
    if (v != fa[u])
      dfs(v), f[u] ^= 1;
}

void Work() {
  dfs(rt1);
  dfs(rt2);
  REP(i, 1, n) if (f[i] != f[i + n]) {
    puts("IMPOSSIBLE");
    return;
  }
  puts("POSSIBLE");
  REP(i, 1, n) if (f[i]) G[i].PB(i + n), G[i + n].PB(i), Ans[i] = -1;
  G[0].PB(rt1);
  G[rt1].PB(0);
  G[0].PB(rt2);
  G[rt2].PB(0);
  Euler(0);
  REP(i, 1, top - 1) if (S[i + 1] == S[i] + n) Ans[S[i]] = 1;
  REP(i, 1, n) printf("%d ", Ans[i]);
  puts("");
}

void Init() {
  read(n);
  REP(i, 1, n) {
    read(fa[i]);
    if (fa[i] == -1)
      rt1 = i;
    else
      G[i].PB(fa[i]), G[fa[i]].PB(i);
  }
  REP(i, n + 1, n * 2) {
    read(fa[i]);
    if (fa[i] == -1)
      rt2 = i;
    else
      fa[i] += n, G[i].PB(fa[i]), G[fa[i]].PB(i);
  }
}

int main() {
  Init();
  Work();
  return 0;
}


Fixed submission:
#include "bits/stdc++.h"

#define PB push_back
#define PF push_front
#define LB lower_bound
#define UB upper_bound
#define fr(x) freopen(x, "r", stdin)
#define fw(x) freopen(x, "w", stdout)
#define iout(x) printf("%d\n", x)
#define lout(x) printf("%lld\n", x)
#define REP(x, l, u) for (int x = (l); x <= (u); x++)
#define RREP(x, l, u) for (int x = (l); x >= (u); x--)
#define mst(x, a) memset(x, a, sizeof(x))
#define PII pair<int, int>
#define PLL pair<ll, ll>
#define MP make_pair
#define se second
#define fi first
#define dbg(x) cout << #x << " = " << (x) << endl;
#define sz(x) ((int)x.size())
#define cl(x) x.clear()

typedef long long ll;
typedef unsigned long long ull;
typedef double db;
typedef long double ld;
using namespace std;

const int maxn = 600010;
const int mod = 1e9 + 7;
const int MAX = 1000000010;
const double eps = 1e-6;
const double PI = acos(-1);

template <typename T> inline void read(T &x) {
  x = 0;
  T f = 1;
  char ch;
  do {
    ch = getchar();
    if (ch == '-')
      f = -1;
  } while (ch < '0' || ch > '9');
  do
    x = x * 10 + ch - '0', ch = getchar();
  while (ch <= '9' && ch >= '0');
  x *= f;
}

template <typename A, typename B> inline void read(A &x, B &y) {
  read(x);
  read(y);
}
template <typename A, typename B, typename C>
inline void read(A &x, B &y, C &z) {
  read(x);
  read(y);
  read(z);
}
template <typename A, typename B, typename C, typename D>
inline void read(A &x, B &y, C &z, D &w) {
  read(x);
  read(y);
  read(z);
  read(w);
}
template <typename A, typename B> inline A fexp(A x, B p) {
  A ans = 1;
  for (; p; p >>= 1, x = 1LL * x * x % mod)
    if (p & 1)
      ans = 1LL * ans * x % mod;
  return ans;
}
template <typename A, typename B> inline A fexp(A x, B p, A mo) {
  A ans = 1;
  for (; p; p >>= 1, x = 1LL * x * x % mo)
    if (p & 1)
      ans = 1LL * ans * x % mo;
  return ans;
}

int n, rt1, rt2;

int fa[maxn];

vector<int> G[maxn];

int f[maxn], Ans[maxn], S[maxn], top;

map<PII, int> mp;

void Euler(int u) {
  for (int i = (int)G[u].size() - 1; i >= 0; i--) {
    int v = G[u][i];
    G[u].pop_back();
    if (!mp[MP(u, v)]) {
      mp[MP(v, u)] = mp[MP(u, v)] = 1;
      Euler(v);
      i = min(i, (int)G[u].size());
    }
  }
  S[++top] = u;
}

void dfs(int u) {
  f[u] = 1;
  for (auto v : G[u])
    if (v != fa[u])
      dfs(v), f[u] ^= 1;
}

void Work() {
  dfs(rt1);
  dfs(rt2);
  REP(i, 1, n) if (f[i] != f[i + n]) {
    puts("IMPOSSIBLE");
    return;
  }
  puts("POSSIBLE");
  REP(i, 1, n) if (f[i]) G[i].PB(i + n), G[i + n].PB(i), Ans[i] = -1;
  G[0].PB(rt1);
  G[rt1].PB(0);
  G[0].PB(rt2);
  G[rt2].PB(0);
  Euler(0);
  REP(i, 1, top - 1) if (S[i + 1] == S[i] + n) Ans[S[i]] = 1;
  REP(i, 1, n) printf("%d ", Ans[i]);
  puts("");
}

void Init() {
  read(n);
  REP(i, 1, n) {
    read(fa[i]);
    if (fa[i] == -1)
      rt1 = i;
    else
      G[i].PB(fa[i]), G[fa[i]].PB(i);
  }
  REP(i, n + 1, n * 2) {
    read(fa[i]);
    if (fa[i] == -1)
      rt2 = i;
    else
      fa[i] += n, G[i].PB(fa[i]), G[fa[i]].PB(i);
  }
}

int main() {
  Init();
  Work();
  return 0;
}