Happy Number (medium)

Problem Statement

Any number will be called a happy number if, after repeatedly replacing it with a number equal to the sum of the square of all of its digits, leads us to number ‘1’. All other (not-happy) numbers will never reach ‘1’. Instead, they will be stuck in a cycle of numbers which does not include ‘1’.

Example 1:

Input: 23   
Output: true (23 is a happy number)  
Explanations: Here are the steps to find out that 23 is a happy number:

$2^2 + 3 ^2$ = 4 + 9 = 13
$1^2 + 3^2$ = 1 + 9 = 10
$1^2 + 0^2$ = 1 + 0 = 1

Example 2:

Input: 12   
Output: false (12 is not a happy number)  
Explanations: Here are the steps to find out that 12 is not a happy number:

$1^2 + 2 ^2$ = 1 + 4 = 5
$5^2$

...

Introduction

Pattern: Sliding Window

Pattern: Two Pointers

Pattern: Fast and Slow Patterns

Pattern: Merge Intervals

Pattern: Cyclic Sort

Pattern: In-place Reversal of a LinkedList

Pattern: Tree Breadth First Search

Pattern: Tree Depth First Search

Pattern: Two Heaps

Pattern: Subsets

Pattern: Modified Binary Search

Pattern: Bitwise XOR

Pattern: Top 'K' Elements

Pattern: K-way merge

Pattern : 0/1 Knapsack (Dynamic Programming)

Pattern: Topological Sort (Graph)

Miscellaneous

Conclusions

Happy Number (medium)

Problem Statement