Leetcode 3291. Minimum Number of Valid Strings to Form Target I

Given words and a target, each valid piece is any prefix of any word; return the minimum number of such prefixes that concatenate to form target, or -1 if impossible. This is a shortest-segmentation problem based on prefix matching (solvable with DP/trie) with target length up to ~5k and total words length up to ~1e5.