LeetCode 1346. Check If N and Its Double Exist

Description

https://leetcode.com/problems/check-if-n-and-its-double-exist/

Given an array arr of integers, check if there exists two integers N and M such that N is the double of M ( i.e. N = 2 * M).

More formally check if there exists 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: N = 10 is the double of M = 5,that is, 10 = 2 * 5.

Example 2:

Input: arr = [7,1,14,11]
Output: true
Explanation: N = 14 is the double of M = 7,that is, 14 = 2 * 7.

Example 3:

Input: arr = [3,1,7,11]
Output: false
Explanation: In this case does not exist N and M, such that N = 2 * M.

Constraints:

  • 2 <= arr.length <= 500
  • -10^3 <= arr[i] <= 10^3

Explanation

Sort the list in order and check if the twice of the element value in the visited set.

Python Solution

class Solution:
    def checkIfExist(self, arr: List[int]) -> bool:
        
        arr_in_order = sorted(arr)
        
        visited = set()
        for num in arr_in_order:
            if num * 2 in visited:
                return True
            
            visited.add(num)
            
        visited = set()
        for num in arr_in_order[::-1]:
            if num * 2 in visited:
                return True
            
            visited.add(num)
            
        return False
            
  • Time Complexity: O(N).
  • Space Complexity: O(N).

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