如何使用swift in time complexity<o(n^2)和space complexity o(n)对整数数组进行按值排序和按重复次数排序

这是我试过的解决方案,但顺序是O(n^2),所以没有通过测试结果。

func sortArrayByValueAndByFrequency(nums : [Int]) {
    var countDict = [Int : Int]()
    var count  = Int()
    var values = Int()
    var output = [Int]()
    for index in 0 ..< nums.count {
        for index2 in 0 ..< nums.count{
            if nums[index2] == nums[index] {
                values = nums[index2]
                count += 1
            }
        }
        countDict[values] = count

        count = 0
    }

    let sortedByKey = countDict.sorted { ($0.key < $1.key)}
    let sortedByValue = sortedByKey.sorted { ($0.value < $1.value)}
    for (k,v) in sortedByValue {
        for _ in 1 ... v {
            output.append(k)
        }
    }

    output.forEach { (orderedNumber) in
        print(orderedNumber)
    }
}

输入/输出示例:

Example array = [1,1,2,3,4,5,5,6,7,7,7,8,9,9,9,20,25,21,20]
Expected output = [2,3,4,6,8,21,25,1,1,5,5,20,20,7,7,7,9,9,9]

example 2 = [1,2,3,4,4,3,3]
output = [1,2,4,4,3,3,3]

这个问题是在hackrank上问我的