Problem
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 <= 2^31 - 1
Solution
/**
* @param {number} num
* @return {string}
*/
const LESS_THAN_20 = ["", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"];
const TENS = ["", "Ten", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"];
const THOUSANDS = ["", "Thousand", "Million", "Billion"];
var numberToWords = function(num) {
if (num == 0) return "Zero";
var i = 0;
var res = "";
while (num > 0) {
if (num % 1000 != 0) // 3 digits a group
res = helper(num % 1000) + THOUSANDS[i] + " " + res;
num = Math.floor(num / 1000);
i++; // cannot put into THOUSANDS[i++] !!! e.x. 1000
}
return res.trim(); // important
}
function helper(num) {
if (num == 0) return ""; // necessary! 50868
else if (num < 20) return LESS_THAN_20[num] + " "; // 1 - 19
else if (num < 100) return TENS[Math.floor(num / 10)] + " " + helper(num % 10); // 20,30,40,50,60,70,80,90
else return LESS_THAN_20[Math.floor(num / 100)] + " Hundred " + helper(num % 100); // > 100
}
Explain:
nope.
Complexity:
- Time complexity : O(n).
- Space complexity : O(n).