Last War Z

Every uppercase letter must start a new word, so the split is unique.

Compare each complete word with the five designated words and record its presence in a bitmask. Process the final word too. Answer YES exactly when at least two bits are set. Substring matches and repeated occurrences are not distinct complete words.

Each character is examined a constant number of times: $O(N)$ time, $O(N)$ space including the input, and $O(1)$ auxiliary space.

There is one full-constraints subtask. The separate naive implementation stores the words and uses a set to remove duplicates. It also passes the full task in $O(N)$ time and $O(N)$ space.

Solution written by GPT