## Integer to English Words

Convert a non-negative integer to its english words representation. Given input is guaranteed to be less than 231 - 1.

For example,

123 -> "One Hundred Twenty Three"
12345 -> "Twelve Thousand Three Hundred Forty Five"
1234567 -> "One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"

## Analysis:

This problem is not difficult but should pay more attention for the corner cases.

General idea is to:

• Split the nums every 3 digits.
• For every 3 digits, write a function to represent into string format
• Between every 3 digits, add the correct "spliter", e.g., thousand, million, etc.
• Take care of the zeros

Please look at the Python code shown below, it should be clear enough for understanding the whole process.

## Code (C++):

class Solution {
public:
string numberThreeDigits(int num, string name_1_9[], string name_10_19[], string name_20_90[]){
string res = "";
if (num / 100 > 0){ res += name_1_9[(num/100)] + " Hundred ";}
num = num % 100;
if (num / 10 > 1) {
res += name_20_90[num/10 - 2] + " ";
num = num%10;
if (num >= 1 ){res += name_1_9[num] + " ";}
} else if (num/10 == 1){
num = num% 10;
res += name_10_19[num] + " ";
} else if (num >= 1 ){
res += name_1_9[num] + " ";
}
return res;
}
string numberToWords(int num){
string name_1_9[] = {"Zero", "One", "Two", "Three", "Four", "Five", "Six", "Seven","Eight","Nine"};
string name_10_19[] = {"Ten", "Eleven", "Twelve","Thirteen","Fourteen", "Fifteen","Sixteen","Seventeen","Eighteen","Nineteen"};
string name_20_90[] = {"Twenty", "Thirty", "Forty","Fifty","Sixty","Seventy","Eighty","Ninety"};
string name_scale[] = {"","Thousand", "Million","Billion"};
vector<int>nums;
while (num/1000 >0){
nums.push_back(num%1000);
num = num/1000;
}
nums.push_back(num);
string res = "";
for (int i=0;i<nums.size();++i){
string tmp = numberThreeDigits(nums[i], name_1_9, name_10_19, name_20_90);
if (tmp != ""){
res = tmp + name_scale[i] + " " + res;
}else if (nums.size()==1){
res = "Zero";
}
}
int sp_pos = res.size()-1;
while (res[sp_pos] == ' '){
sp_pos--;
}
return res.substr(0,sp_pos+1);
}
};

## Code (Python):

class Solution(object):
name_1_9 = ["Zero", "One", "Two", "Three", "Four", "Five", "Six", "Seven","Eight","Nine"]
name_10_19 = ["Ten", "Eleven", "Twelve","Thirteen","Fourteen", "Fifteen","Sixteen","Seventeen","Eighteen","Nineteen"]
name_20_90 = ["Twenty", "Thirty", "Forty","Fifty","Sixty","Seventy","Eighty","Ninety"]
name_scale = ["","Thousand", "Million","Billion"]
def numberThreeDigits(self, num):
res = ""
if num / 100 > 0:
res += self.name_1_9[(num/100)] + " Hundred "
num = num % 100
if num / 10 > 1:
res += self.name_20_90[num/10 - 2] + " "
num = num%10
if num >= 1:
res += self.name_1_9[num] + " "
elif num/10 == 1:
num = num % 10
res += self.name_10_19[num] + " "
elif num >= 1:
res += self.name_1_9[num] + " "
return res
def numberToWords(self, num):
"""
:type num: int
:rtype: str
"""
nums = []
while num/1000 >0:
nums.append(num%1000)
num = num/1000
nums.append(num)
res = ""
for i in range(len(nums)):
tmp = self.numberThreeDigits(nums[i])
if tmp != "":
res = tmp + self.name_scale[i] + " " + res
elif len(nums)==1:
res = "Zero"
return res.rstrip()