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Grokking the Coding Interview Patterns

Solution: Integer to English Words

Explore the method to convert any nonnegative integer into its English word form. Understand the role of digits, place values, and special cases in building the word representation. Learn to implement a stepwise approach that handles numbers up to billions with clarity and efficiency.

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Statement

Given a nonnegative integer, num, convert it to its English word representation.

Constraints:

  • 0≤0 \le num ≤231−1\le 2^{31}-1

Solution

To solve this problem, we need to understand the different types of words that can appear in the word representation of a number, which depend on three factors:

  1. Digits: There are ten digits ranging from 0 to 9.

  2. Number of digits: In our case, the maximum number of digits could be 1010 because the input number, num, will be in the range [0, 2147483647].

  3. Positional values: The positional value, also known as place value, of a digit can be ones (units), tens, hundreds, thousands, ten thousands, hundred thousands, millions, ten millions, hundred millions, or billions.

Based on these factors, numbers in different ranges have specific word representations. Here’s a general workflow for converting numbers to their word representation:

  1. Numbers from 00 ...