Integer to English Words - Practice Coding Problems

Integer to English Words - Problem

Convert a non-negative integer num to its English words representation.

Example: Given num = 123, return "One Hundred Twenty Three"

Note: You need to handle numbers from 0 to 2,147,483,647 (2³¹ - 1)

The output should be properly capitalized with spaces between words, and no extra spaces at the beginning or end.

Input & Output

Example 1 — Basic Case

$ Input: num = 123

› Output: One Hundred Twenty Three

💡 Note: 123 = 1 hundred + 20 + 3 → One Hundred Twenty Three

Example 2 — Edge Case Zero

$ Input: num = 0

› Output: Zero

💡 Note: Special case: zero is handled separately

Example 3 — Large Number

$ Input: num = 1234567

› Output: One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven

💡 Note: Break into groups: 1 million + 234 thousand + 567

Constraints

0 ≤ num ≤ 2³¹ - 1
The input is guaranteed to be a valid integer

Visualization

Tap to expand

Understanding the Visualization

Input

Integer number like 123

Process

Convert each digit group to words

Output

English words: One Hundred Twenty Three

Key Takeaway

🎯 Key Insight: Group numbers by thousands and recursively convert each group using lookup arrays

Asked in

M Microsoft 45 F Facebook 38 A Amazon 32 G Google 28

The key insight is to break numbers into groups of thousands (billions, millions, thousands, ones) and handle each group recursively. The optimal approach uses divide and conquer with recursion to process each group separately. Time: O(log n), Space: O(log n)

Common Approaches

Approach	Time	Space	Notes
✓ Brute Force - Giant Lookup Table	O(1)	O(1)	Create massive lookup tables for every possible combination
Divide and Conquer with Recursion	O(log n)	O(log n)	Break number into groups of thousands and handle each group recursively

Brute Force - Giant Lookup Table — Algorithm Steps

Create arrays for all possible number combinations
Use nested if-else to handle each case
Concatenate appropriate strings

Visualization

Tap to expand

Step-by-Step Walkthrough

Create Arrays

Build huge lookup tables for every combination

Nested Conditions

Use complex if-else chains to find right mapping

Result

Return pre-computed string

Code -

solution.c — C

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

char* solution(int num) {
    static char result[1000];
    
    if (num == 0) {
        strcpy(result, "Zero");
        return result;
    }
    
    char* ones[] = {"Zero", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine"};
    char* teens[] = {"Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"};
    char* twenties[] = {"", "", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"};
    
    if (num < 10) {
        strcpy(result, ones[num]);
    } else if (num < 20) {
        strcpy(result, teens[num - 10]);
    } else if (num < 100) {
        int tensDigit = num / 10;
        int onesDigit = num % 10;
        if (onesDigit == 0) {
            strcpy(result, twenties[tensDigit]);
        } else {
            sprintf(result, "%s %s", twenties[tensDigit], ones[onesDigit]);
        }
    } else {
        strcpy(result, "Not fully implemented");
    }
    
    return result;
}

int main() {
    int num;
    scanf("%d", &num);
    printf("%s\n", solution(num));
    return 0;
}

Time & Space Complexity

Time Complexity

⏱️

O(1)

Constant lookup time but with huge constant factor

✓ Linear Growth

Space Complexity

O(1)

Fixed size lookup tables but extremely large

✓ Linear Space

78.4K Views

Medium Frequency

~25 min Avg. Time

1.8K Likes

Ln 1, Col 1

Smart Actions

💡 Explanation

AI Ready

💡 Suggestion Tab to accept Esc to dismiss

// Output will appear here after running code

Code Editor Closed

Click the red button to reopen

Input & Output

Constraints

Visualization

Related Problems

Common Approaches

Brute Force - Giant Lookup Table — Algorithm Steps

Visualization

Code -

Time & Space Complexity

Select Compiler