273 Integer to English Words

273 Integer to English Words

string.trim()is a built-in function that eliminates leading and trailing spaces.
https://www.geeksforgeeks.org/java-string-trim-method-example/




Input: 1， 234， 567
Output: "One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"





这道题就是先把 567 先转化掉， 再 转化 234， 接个 Thousand， 按照 i 的个数 增常，然后再 转化 1， 接个 Million

Input: 123
Output: "One Hundred Twenty Three"
Example 2:

Input: 12 , 345
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"
   
   
1,000,000,000 one billion   
    1,000,000 one million
        1,000 one thousand 
        
class Solution {
    private final String[] LESS_THAN_20 = {"", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"};
    private final String[] TENS = {"", "Ten", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"};
    private final String[] THOUSANDS = {"", "Thousand", "Million", "Billion"};

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

        int i = 0;
        String words = "";
    
        while (num > 0) {
            if (num % 1000 != 0){
            words = helper(num % 1000) +THOUSANDS[i] + " " + words;
            }
            num = num /1000;
            i++;
        }
    
        return words.trim();
    }

    private String helper(int num) {
        if (num == 0){
            return "";
        }else if (num < 20){
            return LESS_THAN_20[num] + " ";
        }else if (num < 100){
            return TENS[num / 10] + " " + helper(num % 10);
        }else{
            return LESS_THAN_20[num / 100] + " Hundred " + helper(num % 100);
        }
    }
}


// 


2. 
  number = 123 
  123 % 1000 = 123 
  helper(123 % 1000) + thousand[0] + 
  
  helper(123)
  123/100 = 1 (one from less than 20 [1] ) hundred + helper(123 % 100)
  
  helper(123 % 100 = 23)
  tens(23/20= 2) twenty + helper(23 % 10)
  
  
  
  
  
  
  
  
1. 
  
num = 5000
5000 % 1000 = 0

num = num / 1000 = 5000/1000 = 5 
  i = 1 
  
  num = 5 > 0 
  5 % 1000 = 5 
  helper(5 % 1000) + thousand[1] + "" + words = five thousand 
  

1,234,567

 

One (million) 

234(thousand)

567() 

 

I = 0

Words = “”

 

Words = helper(1,234,567 % 1000) + thousand[I = 1] + “” + words

 

helper(1,234,567 % 1000 = 567 ) + thousand[I = 0] + “” + words 

 

Num = num /1000 = 1, 234

I++.

I = 1 

 

 

 

=================

 

1,234,567 > 0 

1,234,567 = 1234 * 1000 + 567

 

1,234,567 % 1000 = 567 

 

helper(567) + thousand(I = 0 ) + “” + words 

===========================

helper(567) = five hundred sixty seven 

 

helper(567) 

 

567 > 20 

567 > 100

Less than twenty(567 / 100) + “hundred” + helper(567 % 100)

 

Less than twenty(567/ 100) = “five”

 

helper(567 % 100) = helper(67) = sixty seven 

 

helper(67) 

67 > 20 

67 > 100 

 

tens(67 /100= 6) + “” + helper(67 % 10 = 7)

tens(6) = sixty 

 

helper(7) = 

7 < 20 

= less than twenty (7) + “” = “seven”

 

===========================

thousand[I] = thousand 

Words = five hundred sixty-seven 

 

Words = helper(1,234 % 1000 = 234 ) + thousand[I = 1] + “” + words

 

Num = num / 1000 = 1

I++.

I = 2 

====================

 

helper(1,234 % 1000 = 234 ) 

helper(234) = 

Same as above for getting 567 , we got two hundred thirty four 

 

thousand[I = 1] = thousand 

 

So words =  two hundred thirty four  + thousand 

=====

 

Num = 1 > 0 

 

Num % 1000 = 1 != 0 

Words =  two hundred thirty four +  thousand  +  five hundred sixty seven 

Words = helper(num % 1000 = 1) + thousand (2) + “” + words 

 

 thousand (2) = million 

 

Words = one million +   two hundred thirty four +  thousand  +  five hundred sixty seven

 

num = num / 1000 = 1 / 1000 = 0

 

Return Words = one million +   two hundred thirty four +  thousand  +  five hundred sixty seven

 

 

 

 

先用recursive方法，followup是iterative的 

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"