Grokking Dynamic Programming Patterns for Coding Interviews

Solution: Longest Common Subsequence

## Problem Statement
Given two strings 's1' and 's2', find the length of the longest subsequence which is common in both the strings.

A [subsequence](https://en.wikipedia.org/wiki/Subsequence) is a sequence that can be derived from another sequence by deleting some or no elements without changing the order of the remaining elements. 

**Example 1:**
```
Input: s1 = "abdca"
       s2 = "cbda"
Output: 3
Explanation: The longest common subsequence is "bda".
```

**Example 2:**
```
Input: s1 = "passport"
       s2 = "ppsspt"
Output: 5
Explanation: The longest common subsequence is "psspt".
```