Given two arrays of single digits nums1 and nums2 and integer k, create the maximum number of length k using digits from both arrays while preserving relative order within each array. Return it as a digit string. Input: '[nums1], [nums2], k'.
Input: '[nums1], [nums2], k'.
Output: Digit string of length k.
Input: [3,4,6,5], [9,1,2,5,8,3], 5
Output: "98653"
Explanation: Max number of length 5.Input: [6,7], [6,0,4], 5
Output: "67604"
Explanation: Length-5 max.Input: [3,9], [8,9], 3
Output: "989"
Explanation: Length-3 max.0<=nums[i]<=91<=k<=nums1.length+nums2.length