Problem Description
You are given a string array words and a binary array groups both of length n, where words[i] is associated with groups[i]. Your task is to select the longest alternating subsequence from words. A subsequence of words is alternating if for any two consecutive strings in the sequence, their corresponding elements in the binary array groups differ. Essentially, you are to choose strings such that adjacent elements have non-matching corresponding bits in the groups array. Return the selected subsequence. If there are multiple answers, return any of them.
Key Insights
- A subsequence must consist of words whose corresponding group values alternate (0, 1 or 1, 0).
- The problem can be solved with a simple linear scan of the input arrays.
- Since the elements in words are distinct, we can safely track the last added element to ensure alternation.
Space and Time Complexity
Time Complexity: O(n)
Space Complexity: O(n)
Solution
To solve the problem, we can iterate through the words and groups arrays simultaneously. We maintain a result list to store the valid subsequence. We start by adding the first word to the result. Then, for each subsequent word, we check if its corresponding group value is different from the last added word's group value. If so, we add the current word to the result list. This approach ensures we only traverse the arrays once, yielding an efficient solution.