My journey in competitive programming

1. Letter Combinations of a Phone Number:

This problem asks you to take a string of digits (like "23") and generate all possible letter combinations based on a phone keypad.

Example:

Input: "23"
Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"]

How to solve:

1. Use a dictionary to map digits to their corresponding letters.
2. Use backtracking to explore all possible combinations of letters for the input digits.

2. Generate Parentheses:

This problem asks you to generate all combinations of n pairs of valid parentheses.

Example:

Input: n = 3
Output: ["((()))", "(()())", "(())()", "()(())", "()()()"]

How to solve:

1. Use backtracking to explore all possible ways of placing open '(' and close ')' brackets.
2. The combination is valid by tracking the number of open and close brackets.