Need help with figuring out best possible solution for this problem: There are two strings of same length representing numbers, we can swap the elements at corresponding index in both strings. There exist some integer k such that k swaps results in strings with minimum absolute difference. Task is to find k. Example of one of possible swap: s = "123" and t = "456" -> swap at index 0 makes s = "423" and t = "156" -> abs diff is 267 a possible solution is using back tracking but there should be better solution for this.

A follow-up question, given some k we want to find minimum possible absolute difference after k swaps.