Possible solution to https://codeforces.com/problemset/problem/1620/E?mobile

replace_num(v2).cpp

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

inline int *new_query(int op, int x, int y);
inline void clear_queries(int **queries, int cnt);
int **get_queries(int cnt);
inline int get_replaced_val(unordered_map<int, int> &ref, int query);


int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);

  int cnt{};
  cin >> cnt;

  int **queries = get_queries(cnt);
  int *query = nullptr;
  unordered_map<int, int> replace_ref{};

  vector<int> result{};
  for (int i = cnt - 1; i >= 0; --i) {
    query = queries[i];
    if (query[0] == 1) {
      result.push_back(get_replaced_val(replace_ref, query[1]));
    } else {
      replace_ref[query[1]] = query[2];
    }
  }
  for (int i = result.size() - 1; i >= 0; --i)
    cout << result[i] << ' ';

  clear_queries(queries, cnt);
  return 0;
}

inline int *new_query(int op, int x, int y = 0) {
  int *query = new int[3];
  query[0] = op;
  query[1] = x;
  query[2] = y;
  return query;
}

inline void clear_queries(int **queries, int cnt) {
  for (int i = 0; i < cnt; ++i)
    delete queries[i];
  delete[] queries;
}

int **get_queries(int cnt) {
  int **queries = new int *[cnt];
  int op, x, y;
  for (int i = 0; i < cnt; ++i) {
    cin >> op >> x;
    if (op == 1) {
      queries[i] = new_query(op, x);
    } else {
      cin >> y;
      queries[i] = new_query(op, x, y);
    }
  }
  return queries;
}

inline int get_replaced_val(unordered_map<int, int> &ref, int query) {
  try {
    while (ref[query] && ref[query] != query)
      query = ref[query];
  } catch(exception &e) {
    return query;
  }
  return query;
}

replace_num(v3|AC).cpp

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

inline int *new_query(int op, int x, int y);
inline void clear_queries(int **queries, int cnt);
int **get_queries(int cnt);

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  cout.tie(NULL);

  int cnt{};
  cin >> cnt;

  int **queries = get_queries(cnt);
  int *query = nullptr;
  int *replace_ref = new int[5000001];
  for (int i=0; i <= 500000; ++i) replace_ref[i] = i;

  vector<int> result{};
  for (int i = cnt - 1; i >= 0; --i) {
    query = queries[i];
    if (query[0] == 1) {
      result.push_back(replace_ref[query[1]]);
    } else {
      replace_ref[query[1]] = replace_ref[query[2]];
    }
  }
  for (int i = result.size() - 1; i >= 0; --i)
    cout << result[i] << ' ';

  delete[] replace_ref;
  clear_queries(queries, cnt);
  return 0;
}

inline int *new_query(int op, int x, int y = 0) {
  int *query = new int[3];
  query[0] = op;
  query[1] = x;
  query[2] = y;
  return query;
}

inline void clear_queries(int **queries, int cnt) {
  for (int i = 0; i < cnt; ++i)
    delete[] queries[i];
  delete[] queries;
}

int **get_queries(int cnt) {
  int **queries = new int *[cnt];
  int op, x, y;
  for (int i = 0; i < cnt; ++i) {
    cin >> op >> x;
    if (op == 1) {
      queries[i] = new_query(op, x);
    } else {
      cin >> y;
      queries[i] = new_query(op, x, y);
    }
  }
  return queries;
}

replace_number.c

#include <stdio.h>

#define MAX_SIZE 500000

int find_val_id(int* ids, int ids_size, int val);

int main() {
  int result[MAX_SIZE];
  int num_ids[MAX_SIZE];
  int result_end = -1;
  int num_id_end = -1;

  int operation_type = 0;
  int append_num = 0, find_num = 0, replace_num = 0;
  int current_id = -1, find_id = -1, replace_id = -1;
  int query_num = 0;
  scanf("%d", &query_num);
  for (int i = 0; i < query_num; ++i) {
    scanf("%d", &operation_type);
    if (operation_type == 1) {
      scanf("%d", &append_num);
      if (result_end == -1 && num_id_end == -1) {
        result_end = 0;
        num_id_end = 0;
      }
      current_id = find_val_id(num_ids, num_id_end, append_num);
      if (current_id == -1) {
        num_ids[num_id_end++] = append_num;
        current_id = num_id_end - 1;
      }
      result[result_end++] = current_id;
    } else if (operation_type == 2) {
      scanf("%d %d", &find_num, &replace_num);
      find_id = find_val_id(num_ids, num_id_end, find_num);;
      if (find_id != -1) {
        replace_id = find_val_id(num_ids, num_id_end, replace_num);
        if (replace_id == -1) {
          num_ids[find_id] = replace_num;
        } else {
          for (int m = 0; m < result_end; ++m) {
            if (result[m] == find_id) {
              result[m] = replace_id;
            }
          }
        }
      }
    }
  }
  for (int j = 0; j < result_end; ++j) {
    printf("%d", num_ids[result[j]]);
    if (j != result_end-1) {
      putchar(' ');
    }
  }
  return 0;
}

int find_val_id(int* ids, int ids_size, int val) {
  for (int i = 0; i < ids_size; ++i) {
    if (ids[i] == val) {
      return i;
    }
  }
  return -1;
}

replace_number.cpp

#include <iostream>
#include <vector>

int main() {
  int query_num{};
  std::cin >> query_num;
  std::vector<int> result{};
  for (int i=0; i < query_num; i++) {
    int operation_type{};
    std::cin >> operation_type;
    if (operation_type == 1) {
      int append{};
      std::cin >> append;
      result.push_back(append);
    } else {
      int find_num{}, replace_num{};
      std::cin >> find_num >> replace_num;
      for (auto &x: result) if (x == find_num) x = replace_num;
    }
  }
  for (auto x: result)
    std::cout << x << ' ';

  return 0;
}