Longest common subsequence: Write a function to find the longest common subsequence between two strings, and analyze the time and space complexity of your solution.

Longest palindromic substring: Write a function to find the longest palindromic substring in a given string, and analyze the time and space complexity of your solution.

Regular expression matching: Implement a function to match a regular expression pattern to a string, and analyze the time and space complexity of your solution.

Subarray sum: Write a function to find the subarray with the maximum sum in an array, and analyze the time and space complexity of your solution.

Two sum: Write a function to find two numbers in an array that sum to a given target, and analyze the time and space complexity of your solution.