# Integer to English Words

This page explains Java solution to problem `Integer to English Words` using `Math`.

## Problem Statement

Convert a non-negative integer to its english words representation. Given input is guaranteed to be less than `231 - 1`.

Example 1:

Input: 123
Output: One Hundred Twenty Three

Example 2:

Input: 12345
Output: Twelve Thousand Three Hundred Forty Five

Example 3:

Input: 1234567891
Output: One Billion Two Hundred Thirty Four Million Five Hundred Sixty Seven Thousand Eight Hundred Ninety One

## Solution

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``````
package com.vc.hard;

class IntegerToEnglishWords {
private String[] belowTen = {"", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine"};
private String[] belowTwenty = {"Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"};
private String[] belowHundred = {"", "Ten", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"};

public String numberToWords(int num) {
if(num == 0) return "Zero";
else return helper(num);
}

private String helper(int num) {
String str = "";
if(num < 10) str = belowTen[num % 10];
else if(num < 20) str = belowTwenty[num % 10] ;
else if(num < 100) str = belowHundred[num / 10] +" "+helper(num % 10);
else if(num < 1000) str = helper(num / 100) +" Hundred "+helper(num % 100);
else if(num < 1_000_000) str = helper(num / 1000) +" Thousand "+helper(num % 1000);
else if(num < 1_000_000_000) str = helper(num / 1_000_000) +" Million "+helper(num % 1_000_000);
else str = helper(num / 1_000_000_000) +" Billion "+helper(num % 1_000_000_000);
return str.trim();
}
}
``````

## Time Complexity

O(N) Where
N is total number of elements in an input string

O(1)