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

December LeetCoding Challenge 1

Description

Check If N and Its Double Exist

Given an array arr of integers, check if there exist two indices i and j such that :

• i != j
• 0 <= i, j < arr.length
• arr[i] == 2 * arr[j]

Example 1:

Input: arr = [10,2,5,3]
Output: true
Explanation: For i = 0 and j = 2, arr[i] == 10 == 2 * 5 == 2 * arr[j]

Example 2:

Input: arr = [3,1,7,11]
Output: false
Explanation: There is no i and j that satisfy the conditions.

Constraints:

• 2 <= arr.length <= 500
• -103 <= arr[i] <= 103

Solution

class Solution {
public:
  bool checkIfExist(vector<int>& arr) {
    map<int, int> st;
    for(auto i : arr) {
      st[i] += 1;;
    }
    for(auto i : arr) {
      if(i && st.count(i * 2)) return true;
      if(!i && st[i] > 1)return true;
    }
    return false;
  }
};