Find if all numbers appear an even number of times
package _interview_question /** * Given a list/array of integers, return a boolean that states whether all numbers appear an even number of times. Example 1: Input: [3, 1, 2, 1, 2, 3] Output: true Example 2: Input: [1, 2, 1] Output: false Example 3: Input: [1, 2, 3] Output: false * */ class Solution4 { fun findAllIfAppearEvenTime(nums: IntArray): Boolean { /* method 1: Time complexity: O(n), Space complexity: O(n) * */ val map = HashMap<Int, Int>() for (num in nums) { map.put(num, map.getOrDefault(num, 0) + 1) } for (item in map) { if (item.value % 2 != 0) { return false } } return true /* * method 2: Time complexity: O(nlogn), Space complexity: O(1) * */ if (nums.size % 2 != 0) { return false } nums.sort() var sameNumAppearCount = 1 for (i in 0 until nums.size - 1) { if (nums[i] == nums[i + 1]) { sameNumAppearCount++ } else { if (sameNumAppearCount % 2 != 0) { return false } else { sameNumAppearCount = 1 } } } return true } }