Today I have done leetcode's September LeetCoding Challenge with cpp.

September LeetCoding Challenge 15

Description

Find Original Array From Doubled Array

An integer array original is transformed into a doubled array changed by appending twice the value of every element in original, and then randomly shuffling the resulting array.

Given an array changed, return original if changed is a doubled array. If changed is not a doubled array, return an empty array. The elements in original may be returned in any order.

Example 1:

Input: changed = [1,3,4,2,6,8]
Output: [1,3,4]
Explanation: One possible original array could be [1,3,4]:
- Twice the value of 1 is 1 * 2 = 2.
- Twice the value of 3 is 3 * 2 = 6.
- Twice the value of 4 is 4 * 2 = 8.
Other original arrays could be [4,3,1] or [3,1,4].

Example 2:

Input: changed = [6,3,0,1]
Output: []
Explanation: changed is not a doubled array.

Example 3:

Input: changed = [1]
Output: []
Explanation: changed is not a doubled array.

Constraints:

• 1 <= changed.length <= 10^5
• 0 <= changed[i] <= 10^5

Solution

auto speedup = [](){
  cin.tie(nullptr);
  cout.tie(nullptr);
  ios::sync_with_stdio(false);
  return 0;
}();
class Solution {
public:
  vector<int> findOriginalArray(vector<int>& changed) {
    if(changed.size() & 1) return {};
    sort(changed.begin(), changed.end());
    int count[100010] = {};
    vector<int> answer;
    for(auto i : changed) {
      if(count[i] == 0) {
        if(i > 50000) return {};
        count[i * 2] -= 1;
      } else {
        count[i] += 1;
        answer.push_back(i / 2);
      }
    }
    for(int i = 0; i < 100001; ++i) {
      if(count[i]) return {};
    }
    return answer;
  }
};

// Accepted
// 178/178 cases passed (245 ms)
// Your runtime beats 99.56 % of cpp submissions
// Your memory usage beats 96.70 % of cpp submissions (117.8 MB)