Happy Number

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Problem

A number is "happy" if repeatedly replacing it with the sum of the squares of its digits eventually reaches 1. If the process loops endlessly without ever reaching 1, the number is not happy. Determine whether a given number is happy.

Examples

Example 1

Input:n = 19

Output:true

19 -> 82 -> 68 -> 100 -> 1.

Example 2

Input:n = 2

Output:false

Constraints

1 <= n <= 2^31 - 1

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How to approach it: the Math & Geometry pattern

A grab-bag of problems solved with numeric or coordinate reasoning rather than a specific data structure — matrix manipulation, simulation, and basic number theory.

Look for this pattern when

The problem operates on a 2-D grid or matrix directly (rotate, transpose, traverse in a pattern).
There's no obvious "textbook" data structure — the problem is really about careful step-by-step simulation.

Read the full Math & Geometry guide →

Video walkthroughs

Original problem on LeetCode ↗