The ultimate guide to coding interviews. Developed by FAANG engineers. Boost problem-solving skills with number theory, dynamic programming, and graph theory. Get interview-ready in just a few hours.

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Whether you’re gearing up for online coding challenges, code-a-thons, or interviews, then this course is for you. With this course, you will solidify your problem-solving skills ensuring a swift sail through any problem. 


You will be tasked with solving some of the most frequently asked questions that are brought up in FAANG interviews. You will start with the concepts of Number Theory and Divide and Conquer, and gradually move towards more complex problems like dynamic programming and graph theory.


With each problem you solve, there will be insightful explanations and full implementation details to really hammer home the concepts. By the time you finish this course, you will have the confidence to solve any problem, no matter the difficulty.

Competitive Programming - Crack Your Coding Interview, C++

# Problem statement
Before the advent of **QWERTY** keyboards, texts and numbers were placed on the same key. For example, **2** had **ABC** and if we wanted to write anything starting with **A**, we needed to type key **2** once. If we wanted to type **B**, key **2** had to be pressed twice, and thrice for typing **C**. Below is a picture of such a keypad.

**Given a keypad as shown in the diagram, and an `n` digit number, list all possible words by pressing these numbers.**

For example, the value of `n = 234`. Then, we can generate the following words:
```
adg adh adi aeg aeh aei afg afh afi bdg bdh bdi beg beh bei bfg bfh bfi cdg cdh cdi ceg ceh cei cfg cfh cfi
```
# Solution: **Recursive approach**
It can be observed that each digit can represent 3 to 4 different alphabets (apart from 0 and 1). The idea is to form a recursive function. Map the number with its string of probable alphabets, i.e., `2` with `abc`, `3` with `def`, etc. The recursive function will try all the alphabets mapped to the current digit in alphabetic order and again call the recursive function for the next digit and print the current output string.

Let's move on to the implementation now.

Solve a problem based on Recursion and Backtracking.

Overview

Number Theory

Number Theory

Divide and Conquer

Greedy Algorithms

Greedy Algorithms

Recursion and Backtracking

Recursion and Backtracking

Dynamic Programming

Graphs

Bonus Lessons

Phone Keypad Problem

Problem statement