Word Matching Between Two Strings

Meta Logistics compares text fields from two logistics systems and needs to identify word occurrences that do not match across the strings. Write a function that returns unmatched words while preserving their left-to-right order.

A word is a maximal sequence of non-whitespace characters. Matching is case sensitive, so Route and route are different words. Each occurrence in one string can match at most one identical occurrence in the other string. Return unmatched occurrences from the first string in their original order, followed by unmatched occurrences from the second string in their original order.

Formal Specification

• Input: two strings, first and second.
• Output: a list of strings containing all unmatched word occurrences.
• Split both strings using standard whitespace behavior, so multiple spaces and leading or trailing whitespace are allowed.
• If every word occurrence matches, return an empty list.

Examples

Example 1

Input: first = "Meta Logistics ships parcels", second = "Meta Logistics tracks routes"
Output: ["ships", "parcels", "tracks", "routes"]

Meta and Logistics match. The remaining words occur in only one string.

Example 2

Input: first = "Route route route", second = "route route"
Output: ["Route", "route"]

Route differs from route, and one lowercase route occurrence remains unmatched.

Constraints

• 0 <= len(first), len(second) <= 10^5
• Each string contains only whitespace and non-whitespace word characters.
• The total number of word occurrences is at most 2 * 10^5.