https://leetcode.com/problems/top-k-frequent-elements/
var myValue: [Int:Int] = [:]
var result: [Int] = []
for num in nums {
myValue[num, default: 0] += 1
}
let a = myValue.sorted { key1, key2 in
key1.value > key2.value
}
for i in 0..<k {
result.append(a[i].key)
}
return result