Given two lists of distinct integers a and b, each sorted in increasing order, return a sorted list of the values that appear in exactly one of them.
Examples
Input: a = [1, 3, 5, 7], b = [3, 4, 7, 9]
Output: [1, 4, 5, 9]
Input: a = [2, 4], b = [2, 4]
Output: []
Constraints
0 <= len(a), len(b) <= 10**5- Target: O(len(a) + len(b)) time, O(1) extra space beyond the output; no sets.
Goals
- Handle three cases per step: smaller in a, smaller in b, equal
- Flush the remainder of whichever list is left