Two players hold racks of letter tiles, given as lowercase strings a and b. They may discard tiles from either rack. Return the minimum total number of tiles that must be discarded so that the two racks contain exactly the same multiset of letters (i.e. become anagrams of each other, possibly both empty).
Examples
Input: a = "hello", b = "help"
Output: 3
Explanation: discard one "l" and the "o" from a, and the "p" from b; both become "hel".
Input: a = "bread", b = "beard"
Output: 0
Constraints
0 <= len(a), len(b) <= 10**5- Target: O(len(a) + len(b)) time, O(26) extra space.
Goals
- Reduce an anagram question to comparing letter counts
- Sum absolute count differences over the union of letters
- Use Counter arithmetic correctly (it drops non-positive counts)