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Integer to English Words

Problem Statement​

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

Example 1:​

Input: num = 123
Output: "One Hundred Twenty Three"

Example 2:​

Input: num = 12345
Output: "Twelve Thousand Three Hundred Forty Five"

Example 3:​

Input: num = 1234567
Output: "One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"

Constraints:​

  • 0 <= num <= 231 - 1

Leetcode Link

Code​

Python
def numberToWords(self, num):
    to19 = 'One Two Three Four Five Six Seven Eight Nine Ten Eleven Twelve ' \
           'Thirteen Fourteen Fifteen Sixteen Seventeen Eighteen Nineteen'.split()
    tens = 'Twenty Thirty Forty Fifty Sixty Seventy Eighty Ninety'.split()
    def words(n):
        if n < 20:
            return to19[n-1:n]
        if n < 100:
            return [tens[n/10-2]] + words(n%10)
        if n < 1000:
            return [to19[n/100-1]] + ['Hundred'] + words(n%100)
        for p, w in enumerate(('Thousand', 'Million', 'Billion'), 1):
            if n < 1000**(p+1):
                return words(n/1000**p) + [w] + words(n%1000**p)
    return ' '.join(words(num)) or 'Zero'