String Matching in an Array (Substring Containment)

Given an array of strings, identify which words appear as substrings of any other word in the array (equivalently, find which words do NOT appear as substrings of any other word). With up to 100 unique lowercase strings of length ≤30, the core task is detecting pairwise substring containment. Optimize beyond the basic O(n^2 * L) brute force approach using techniques such as concatenation with separators and KMP/Z-algorithm, or trie-based methods.