Coding

Convert Digits/Numbers to Words

Asked at

TCS

1Give yourself 5 minutes

2Answer out loud, not in your head

3Then compare with the answer below

The problem

You are given a non-negative integer num with at most 4 digits (0 <= num <= 9999). Your task is to convert this number into its English words representation.

**Input: **num = 7824 Output: "seven thousand eight hundred twenty four" **Explanation: **7824 is read as "seven thousand eight hundred twenty four"

Input: num = 370 **Output: **"three hundred seventy" Explanation: 370 is read as "three hundred seventy"

Input: num = 1001

0 <= num <= 9999
Do not include "and" between words (e.g., write "one hundred one", not "one hundred and one")
The output should be all lowercase with single spaces between words

cpp

class Solution {
public:
    string numberToWords(int num) {
        // Your code goes here
    }
};

java

class Solution {
    public String numberToWords(int num) {
        // Your code goes here
    }
}

python

class Solution:
    def numberToWords(self, num: int) -> str:
        # Your code goes here

javascript

class Solution {
    numberToWords(num) {
        // Your code goes here
    }
}

csharp

class Solution {
    public string NumberToWords(int num) {
        // Your code goes here
    }
}

func numberToWords(num int) string {

}

Stuck? Show a way to structure it+

01Return zero immediately for input 0.
02Split the number into thousands, hundreds, tens, and ones.
03Use lookup tables for values below 20 and for tens multiples.
04Append only nonzero groups with single-space joining.

Reference answer

Use small lookup tables for 0..19 and the tens (twenty through ninety). For a number below 1000, emit the hundreds part when nonzero, then handle the remainder: numbers below 20 are direct lookups, otherwise emit the tens word and optional ones word. For this problem's four-digit bound, first process num / 1000; if it is nonzero, append its word plus thousand, then process num % 1000. Treat 0 specially as zero, and never append a word for a zero-valued group. This is O(1) time and space for the stated bound. Common formatting pitfalls are extra spaces, using and when the contract forbids it, and emitting zero hundred.

Then expect these follow-ups

How would you extend this to arbitrary 32-bit integers?
Tests: scalable decomposition
How would you parse English words back into a number?
Tests: stateful parsing

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