Integer to English Words

Integer to English Words

1. What is this problem about?

The Integer to English Words interview question is a high-level string formatting challenge. You are given a non-negative integer and must convert it to its English words representation. For example, 123 becomes "One Hundred Twenty Three" and 12345 becomes "Twelve Thousand Three Hundred Forty Five."

2. Why is this asked in interviews?

Tech giants like Amazon, Google, and Apple use this Integer to English Words coding problem to test a candidate's ability to handle complex nested logic and string processing. It evaluations your attention to detail regarding spaces, zero-handling, and group naming (Thousands, Millions, Billions). It’s a rigorous test of clean code and String interview pattern mastery.

3. Algorithmic pattern used

This problem follows the Recursive Grouping pattern.

1. Divide and Conquer: Break the number into groups of three digits (Billions, Millions, Thousands, and the remainder).
2. Helper Function: Write a function convert(num) that handles any number less than 1000.
3. Lookup Arrays: Use arrays to store mappings for "Ones" (One, Two...), "Teens" (Ten, Eleven...), and "Tens" (Twenty, Thirty...).
4. Handling Zero: Ensure "Zero" is only returned if the original input is 0.

4. Example explanation

$n = 1,234,567$

1. Process Million group: convert(1) + " Million".
2. Process Thousand group: convert(234) + " Thousand".
   • 234 -> "Two Hundred" + convert(34)
   • 34 -> "Thirty Four"
3. Process remainder: convert(567). Combine: "One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven".

5. Common mistakes candidates make

• Trailing Spaces: Adding an extra space at the end of the string or between words.
• Teens Logic: Not handling the unique "Teens" (11-19) case separately from the "Tens" (20, 30...) + "Ones" logic.
• Large Zero groups: Failing to skip labels like "Thousand" if the group itself is 000.

6. Interview preparation tip

Focus on modularity. Don't try to write one giant function. Split the logic into "Handle Thousands," "Handle Hundreds," and "Handle Tens." This makes your code much easier to debug and explain during an interview.