1346. Check If N and Its Double Exist

• python3
• Review : 20240703

📎 Problem

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

Pseudocode

1. 전부 hash에 넣는다
2. 거기서 비교

Code

solution of leetcode

class Solution:
    def checkIfExist(self, arr: List[int]) -> bool:
    tmp = set()

	for i in arr:
    	if 2*i in tmp or (i%2 == 0 and i/2 in tmp):
        	return True
        tmp.add(i)

Result

solution of leetcode

• Time Complexity: O(n)
• Space Complexity: O(1)