This is an advanced DP problem. However once understood the logic, the coding becomes fairly simple. The most important thing is to understand the states of the DP. Here we are considering `4-D DP`.

Here's the step-by-step approach: 🔃 Define a recursive function that generates all subsequences of a given string. 🔄 At each step of the recursion, we have two choices for each character: either ...

> 原文:[https://www . geesforgeks . org/count-subseries-first-string-anagrams-second-string/](https://www.geeksforgeeks.org/count-subsequences-first-string-anagrams ...

Abstract: We consider the problem of finding the number of subsequences when deleting symbols from a string. We present a framework to find closed-form expressions for the number of subsequences, and ...

LeetCode problem 1930. Unique Length-3 Palindromic Subsequences The goal is to count unique palindromic subsequences of length 3 within the input string. Approach: A HashMap is created to store ...