273.Integer to English Words

Tags: Hard Math String

Links: https://leetcode.com/problems/integer-to-english-words/submissions/

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

Example 4:

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

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class Solution {
 public:
    string digits[20] = {"Zero", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"};
    string tens[10] = {"Zero", "Ten", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"};

    string int2string(int n) {
        if (n >= 1000000000) {
            return int2string(n / 1000000000) + " Billion" + int2string(n % 1000000000);
        } else if (n >= 1000000) {
            return int2string(n / 1000000) + " Million" + int2string(n % 1000000);
        } else if (n >= 1000) {
            return int2string(n / 1000) + " Thousand" + int2string(n % 1000);
        } else if (n >= 100) {
            return int2string(n / 100) + " Hundred" + int2string(n % 100);
        } else if (n >= 20) {
            return  " " + tens[n / 10] + int2string(n % 10);
        } else if (n >= 1) {
            return " " + digits[n];
        } else {
            return "";
        }
    }

    string numberToWords(int num) {
        if (num == 0) {
            return "Zero";
        } else {
            string ret = int2string(num);
            return ret.substr(1, ret.length() - 1);
        }
    }
};

这道题可以和12 integer to roman 和13 roman to integer结合起来。