[Swift]LeetCode321. 拼接最大数 | Create Maximum Number

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Given two arrays of length m and n with digits 0-9 representing two numbers. Create the maximum number of length k <= m + n from digits of the two. The relative order of the digits from the same array must be preserved. Return an array of the k digits.

Note: You should try to optimize your time and space complexity.

Example 1:

[3, 4, 6, 5]
[9, 1, 2, 5, 8, 3]
5
[9, 8, 6, 5, 3]

Example 2:

[6, 7]
[6, 0, 4]
5
[6, 7, 6, 0, 4]

Example 3:

[3, 9]
[8, 9]
3
[9, 8, 9]

---

说明: 请尽可能地优化你算法的时间和空间复杂度。

示例 1:

[3, 4, 6, 5]
[9, 1, 2, 5, 8, 3]
5
[9, 8, 6, 5, 3]

示例 2:

[6, 7]
[6, 0, 4]
5
[6, 7, 6, 0, 4]

示例 3:

[3, 9]
[8, 9]
3
[9, 8, 9]

---

380 ms

class Solution {
    func maxNumber(_ nums1: [Int], _ nums2: [Int], _ k: Int) -> [Int] {
        let m = nums1.count
        let n = nums2.count
        
        var res = [Int]()
        
        let c = max(0, k-n)
        
        for i in c...min(k, m) {
            let r1 = maxNumArr(nums1, i)
            let r2 = maxNumArr(nums2, k-i)
            let tmp = maxNums(r1, r2, k)
            if isGreater(tmp, res, 0, 0) {
                res = tmp
            }
        }
        
        return res
    }
    
    func maxNumArr(_ nums : [Int], _ k : Int) -> [Int] {
        var res = [Int]()
        for i in 0..<nums.count {
            let num = nums[i]
            while !res.isEmpty && num > res.last! && nums.count + res.count > k + i {
                res.removeLast()
            }
            res.append(num)
            continue
        }
        return res
    }
    
    func maxNums(_ num1 : [Int], _ num2 : [Int],_ k : Int) -> [Int] {
        var res = [Int]()
        var i = 0 , j = 0
        for _ in 0..<k {
            if isGreater(num1, num2, i, j) {
                res.append(num1[i])
                i+=1
            }else {
                res.append(num2[j])
                j+=1
            }
        }
        
        return res
    }
    
    func isGreater(_ nums1: [Int], _ nums2 : [Int], _ i : Int, _ j : Int) -> Bool {
        var i = i , j = j
        while i < nums1.count , j < nums2.count && nums1[i] == nums2[j] {
            i+=1
            j+=1
        }
        
        return j == nums2.count || (i < nums1.count && nums1[i] > nums2[j])
    }
}