Problem p02557 (C++) — buggy submission, verdict: Runtime Error

// #define _GLIBCXX_DEBUG // for STL debug (optional)
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstring>
#include <ctime>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <limits>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>
using namespace std;
using ll = long long int;
using int64 = long long int;

template <typename T> void chmax(T &a, T b) { a = max(a, b); }
template <typename T> void chmin(T &a, T b) { a = min(a, b); }
template <typename T> void chadd(T &a, T b) { a = a + b; }

int dx[] = {0, 0, 1, -1};
int dy[] = {1, -1, 0, 0};
const int INF = 1LL << 29;
const ll LONGINF = 1LL << 60;
const ll MOD = 1000000007LL;

int main() {
  int N;
  scanf("%d", &N);

  vector<int> cnt(N + 1), cntB(N + 1);
  vector<int> A(N), B(N);
  vector<set<int>> idx(N + 1);

  for (int i = 0; i < N; i++) {
    scanf("%d", &A[i]);
    cnt[A[i]]++;
    idx[A[i]].emplace(i);
  }
  for (int i = 0; i < N; i++) {
    scanf("%d", &B[i]);
    cnt[B[i]]++;
    cntB[B[i]]++;
  }

  for (int i = 0; i <= N; i++) {
    if (cnt[i] > N) {
      puts("No");
      return 0;
    }
  }

  vector<int> ord(N);
  iota(ord.begin(), ord.end(), 0);
  sort(ord.begin(), ord.end(), [&](auto x, auto y) { return cnt[x] > cnt[y]; });

  vector<int> ans(N, -1);
  set<int> S;
  for (int i = 0; i < N; i++)
    S.emplace(i);

  for (int i = 0; i < N; i++) {
    // for(int j=0; j<N; j++) fprintf(stderr, "%d%c", ans[j], " \\n"[j + 1 ==
    // N]);

    if (i == 0 or B[i - 1] != B[i]) {
      for (auto j : idx[B[i]]) {
        S.erase(j);
      }
    }

    if (S.empty()) {
      assert(idx[B[i]].size() > 0);
      int k = *idx[B[i]].begin();
      // fprintf(stderr, "same %d %d\\n", i, k);
      ans[k] = B[i];
      idx[B[i]].erase(k);
      S.erase(k);
    } else {
      int k = *S.rbegin();
      ans[k] = B[i];
      idx[A[k]].erase(k);
      S.erase(k);
    }

    if (i == N - 1 or B[i] != B[i + 1]) {
      for (auto j : idx[B[i]]) {
        if (ans[j] == -1)
          S.emplace(j);
      }
    }
  }

  set<int> match;
  for (int i = 0; i < N; i++) {
    assert(ans[i] != -1);
    if (A[i] == ans[i]) {
      match.emplace(i);
    }
  }

  while (match.size()) {
    if (match.size() == 1)
      break;
    int x = *match.begin(), y = *match.rbegin();
    if (A[x] == A[y])
      break;
    swap(ans[x], ans[y]);
    match.erase(x);
    match.erase(y);
  }

  while (match.size()) {
    int x = *match.begin();
    int y = rand() % N;
    if (ans[x] == A[y])
      continue;
    if (ans[y] == A[x])
      continue;
    swap(ans[x], ans[y]);
    match.erase(x);
  }

  puts("Yes");
  for (int i = 0; i < N; i++)
    printf("%d%c", ans[i], " \\n"[i + 1 == N]);
  return 0;
}


Error: WA

Fixed submission:

// #define _GLIBCXX_DEBUG // for STL debug (optional)
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cfloat>
#include <climits>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstring>
#include <ctime>
#include <deque>
#include <fstream>
#include <functional>
#include <iomanip>
#include <iostream>
#include <limits>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <utility>
#include <vector>
using namespace std;
using ll = long long int;
using int64 = long long int;

template <typename T> void chmax(T &a, T b) { a = max(a, b); }
template <typename T> void chmin(T &a, T b) { a = min(a, b); }
template <typename T> void chadd(T &a, T b) { a = a + b; }

int dx[] = {0, 0, 1, -1};
int dy[] = {1, -1, 0, 0};
const int INF = 1LL << 29;
const ll LONGINF = 1LL << 60;
const ll MOD = 1000000007LL;

int main() {
  int N;
  scanf("%d", &N);

  vector<int> cnt(N + 1), cntB(N + 1);
  vector<int> A(N), B(N);
  vector<set<int>> idx(N + 1);

  for (int i = 0; i < N; i++) {
    scanf("%d", &A[i]);
    cnt[A[i]]++;
    idx[A[i]].emplace(i);
  }
  for (int i = 0; i < N; i++) {
    scanf("%d", &B[i]);
    cnt[B[i]]++;
    cntB[B[i]]++;
  }

  for (int i = 0; i <= N; i++) {
    if (cnt[i] > N) {
      puts("No");
      return 0;
    }
  }

  vector<int> ord(N);
  iota(ord.begin(), ord.end(), 0);
  sort(ord.begin(), ord.end(), [&](auto x, auto y) { return cnt[x] > cnt[y]; });

  vector<int> ans(N, -1);
  set<int> S;
  for (int i = 0; i < N; i++)
    S.emplace(i);

  for (int i = 0; i < N; i++) {
    // for(int j=0; j<N; j++) fprintf(stderr, "%d%c", ans[j], " \\n"[j + 1 ==
    // N]);

    if (i == 0 or B[i - 1] != B[i]) {
      for (auto j : idx[B[i]]) {
        S.erase(j);
      }
    }

    if (S.empty()) {
      assert(idx[B[i]].size() > 0);
      int k = *idx[B[i]].begin();
      // fprintf(stderr, "same %d %d\\n", i, k);
      ans[k] = B[i];
      S.erase(k);
    } else {
      int k = *S.rbegin();
      ans[k] = B[i];
      idx[A[k]].erase(k);
      S.erase(k);
    }

    if (i == N - 1 or B[i] != B[i + 1]) {
      for (auto j : idx[B[i]]) {
        if (ans[j] == -1)
          S.emplace(j);
      }
    }
  }

  set<int> match;
  for (int i = 0; i < N; i++) {
    assert(ans[i] != -1);
    if (A[i] == ans[i]) {
      match.emplace(i);
    }
  }

  while (match.size()) {
    if (match.size() == 1)
      break;
    int x = *match.begin(), y = *match.rbegin();
    if (A[x] == A[y])
      break;
    swap(ans[x], ans[y]);
    match.erase(x);
    match.erase(y);
  }

  while (match.size()) {
    int x = *match.begin();
    int y = rand() % N;
    if (ans[x] == A[y])
      continue;
    if (ans[y] == A[x])
      continue;
    swap(ans[x], ans[y]);
    match.erase(x);
  }

  puts("Yes");
  for (int i = 0; i < N; i++)
    printf("%d%c", ans[i], " \\n"[i + 1 == N]);
  return 0;
}