Integer to English Words

Desicription

Convert a non-negative integer to its english words representation. Given input is guaranteed to be less than 2^31 - 1.

Example 1:

1
2
Input: 123
Output: "One Hundred Twenty Three"

Example 2:

1
2
Input: 12345
Output: "Twelve Thousand Three Hundred Forty Five"

Example 3:

1
2
Input: 1234567
Output: "One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"

Example 4:

1
2
Input: 1234567891
Output: "One Billion Two Hundred Thirty Four Million Five Hundred Sixty Seven Thousand Eight Hundred Ninety One"

Solution

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
class Solution {
private:
const vector<string> one_to_nineteen = {
"",
"One",
"Two",
"Three",
"Four",
"Five",
"Six",
"Seven",
"Eight",
"Nine",
"Ten",
"Eleven",
"Twelve",
"Thirteen",
"Fourteen",
"Fifteen",
"Sixteen",
"Seventeen",
"Eighteen",
"Nineteen"
};

const vector<string> twenty_to_ninety = {
"",
"",
"Twenty",
"Thirty",
"Forty",
"Fifty",
"Sixty",
"Seventy",
"Eighty",
"Ninety"
};

string get_words(int num) {
if(num >= (int)1e9) {
return get_words(num / (int)1e9) + " Billion" + get_words(num % (int)1e9);
} else if(num >= (int)1e6) {
return get_words(num / (int)1e6) + " Million" + get_words(num % (int)1e6);
} else if(num >= (int)1e3) {
return get_words(num / (int)1e3) + " Thousand" + get_words(num % (int)1e3);
} else if(num >= (int)1e2) {
return get_words(num / (int)1e2) + " Hundred" + get_words(num % (int)1e2);
} else if(num >= 20) {
return string(" ") + twenty_to_ninety[num / 10] + get_words(num % 10);
} else if(num >= 1) {
return string(" ") + one_to_nineteen[num];
} else {
return string("");
}
}

public:
string numberToWords(int num) {
if(num == 0) {
return "Zero";
} else {
return get_words(num).substr(1);
}
}
};