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Solution: Distinct Subsequences

Understand how to solve the distinct subsequences problem where you count how many subsequences of string s match string t exactly. Learn an efficient dynamic programming technique that uses a 1D array for space optimization, iterating strings in reverse to track subsequence counts. This lesson helps you develop a strong grasp of DP optimization in string matching problems.

Statement

Given two strings, s and t, determine how many distinct subsequences of s match t exactly.

Note: A subsequence is formed by deleting zero or more characters from s without changing the relative order of the remaining characters.

You may assume the result will always fit within a 3232-bit signed integer.

Constraints:

  • 11 \leq s.length, t.length 1000\leq 1000 ...