[swift] LeetCode 347. Top K Frequent Elements

Given a non-empty array of integers, return the k most frequent elements.

For example,

Given [1,1,1,2,2,3] and k = 2, return [1,2].

Note:

You may assume k is always valid, 1 ≤ k ≤ number of unique elements.

Your algorithm’s time complexity must be better than O(n log n), where n is the array’s size.

func topKFrequent(_ nums: [Int], _ k: Int) -> [Int] {
    var dict = [Int:Int]()
    nums.forEach {
        dict[$0] = (dict[$0] == nil ? 0 : dict[$0]! ) + 1
    }
 
    return dict.sorted(by:  { $0.value > $1.value } )[0..<k].map({$0.key})
}