1346. Check If N and Its Double Exist

QUESTION:

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

EXPLANATION:

easy的题目, 一个for循环就能解决.

SOLUTION:

class Solution {
    func checkIfExist(_ arr: [Int]) -> Bool {
        var set:Set<Int> = Set()
        for a in arr {
            if set.contains(a * 2) || (a % 2 == 0 && set.contains(a/2)) {
                return true
            } else {
                set.insert(a)
            }
        }
        return false
    }
}
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