Problem of The Day: Integer to English Words

Problem Statement

Notes:

• Need to review this problem

Editorial

Approach 1: Recursive Approach

class Solution:
    # Arrays to store words for numbers less than 10, 20, and 100
    below_ten = ["", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine"]
    below_twenty = ["Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"]
    below_hundred = ["", "Ten", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"]

    # Main function to convert a number to English words
    def numberToWords(self, num: int) -> str:
        # Handle the special case where the number is zero
        if num == 0:
            return "Zero"
        # Call the helper function to start the conversion
        return self._convert_to_words(num)

    # Recursive function to convert numbers to words
    # Handles numbers based on their ranges: <10, <20, <100, <1000, <1000000, <1000000000, and >=1000000000
    def _convert_to_words(self, num: int) -> str:
        if num < 10:
            return self.below_ten[num]
        if num < 20:
            return self.below_twenty[num - 10]
        if num < 100:
            return self.below_hundred[num // 10] + (" " + self._convert_to_words(num % 10) if num % 10 != 0 else "")
        if num < 1000:
            return self._convert_to_words(num // 100) + " Hundred" + (" " + self._convert_to_words(num % 100) if num % 100 != 0 else "")
        if num < 1000000:
            return self._convert_to_words(num // 1000) + " Thousand" + (" " + self._convert_to_words(num % 1000) if num % 1000 != 0 else "")
        if num < 1000000000:
            return self._convert_to_words(num // 1000000) + " Million" + (" " + self._convert_to_words(num % 1000000) if num % 1000000 != 0 else "")
        return self._convert_to_words(num // 1000000000) + " Billion" + (" " + self._convert_to_words(num % 1000000000) if num % 1000000000 != 0 else "")

Approach 2: Iterative Approach

class Solution:
    def numberToWords(self, num: int) -> str:
        # Handle the special case where the number is zero
        if num == 0:
            return "Zero"

        # Arrays to store words for single digits, tens, and thousands
        ones = ["", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"]
        tens = ["", "", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"]
        thousands = ["", "Thousand", "Million", "Billion"]

        # StringBuilder to accumulate the result
        result = ""
        group_index = 0

        # Process the number in chunks of 1000
        while num > 0:
            # Process the last three digits
            if num % 1000 != 0:
                group_result = ""
                part = num % 1000

                # Handle hundreds
                if part >= 100:
                    group_result += ones[part // 100] + " Hundred "
                    part %= 100

                # Handle tens and units
                if part >= 20:
                    group_result += tens[part // 10] + " "
                    part %= 10

                # Handle units
                if part > 0:
                    group_result += ones[part] + " "

                # Append the scale (thousand, million, billion) for the current group
                group_result += thousands[group_index] + " "
                # Insert the group result at the beginning of the final result
                result = group_result + result
            # Move to the next chunk of 1000
            num //= 1000
            group_index += 1

        return result.strip()

Approach 3: Pair-Based Approach

class Solution:
    # Dictionary to store words for numbers
    number_to_words_map = {
        1000000000: "Billion", 1000000: "Million", 1000: "Thousand",
        100: "Hundred", 90: "Ninety", 80: "Eighty", 70: "Seventy",
        60: "Sixty", 50: "Fifty", 40: "Forty", 30: "Thirty",
        20: "Twenty", 19: "Nineteen", 18: "Eighteen", 17: "Seventeen",
        16: "Sixteen", 15: "Fifteen", 14: "Fourteen", 13: "Thirteen",
        12: "Twelve", 11: "Eleven", 10: "Ten", 9: "Nine", 8: "Eight",
        7: "Seven", 6: "Six", 5: "Five", 4: "Four", 3: "Three",
        2: "Two", 1: "One"
    }

    def numberToWords(self, num: int) -> str:
        if num == 0:
            return "Zero"

        for value, word in self.number_to_words_map.items():
            # Check if the number is greater than or equal to the current unit
            if num >= value:
                # Convert the quotient to words if the current unit is 100 or greater
                prefix = (self.numberToWords(num // value) + " ") if num >= 100 else ""

                # Get the word for the current unit
                unit = word

                # Convert the remainder to words if it's not zero
                suffix = "" if num % value == 0 else " " + self.numberToWords(num % value)

                return prefix + unit + suffix

        return ""