String Pattern Partition

Given two strings, represent the target string as a minimum sequence of substrings indexed from the source string. A follow-up deletes one character and asks for the new minimum partition. Requirements Inputs are two strings: a source string a and a target string b. Return a list of index ranges into a whose concatenated substrings represent b. Example framing: a = "abcdbcd", b = "sabcd", with an index-range style output such as [[1, 3], [4, 4], [2, 4]]. The exact indexing convention and how to handle a target character absent from a should be clarified before coding. Optimize for the minimum number of partitions. Follow-up: after deleting one character, recompute the minimum partition result. Notes This is a string-cover / segmentation prompt. A direct approach precomputes all source substrings, then runs DP over target positions: dp[i] = min(dp[j] + 1) if b[j:i] appears in a. For larger inputs, use a trie, suffix automaton, suffix array, or rolling-hash lookup to find source-substring matches starting at each target position without materializing every substring. The reported example is ambiguous because the target contains a character not present in the source. Clarify whether unmatched characters are allowed, whether they imply failure, and whether ranges are 0-based or 1-based inclusive. The deletion follow-up can often be answered by recomputing DP if constraints are small; for large strings, discuss incremental DP invalidation around the deleted position. Preparation Implement the clean DP version first. Prepare tests for absent characters, repeated source substrings, tie-breaking among equal partition counts, empty target, and deletion at the beginning / middle / end.