• Time:Time:
• Space:Space:

C++

``````class Solution {
public:
string numberToWords(int num) {
if (num == 0)
return "Zero";
return helper(num);
}

private:
const vector<string> belowTwenty{
"",        "One",     "Two",       "Three",    "Four",
"Five",    "Six",     "Seven",     "Eight",    "Nine",
"Ten",     "Eleven",  "Twelve",    "Thirteen", "Fourteen",
"Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"};
const vector<string> tens{"",      "",      "Twenty",  "Thirty", "Forty",
"Fifty", "Sixty", "Seventy", "Eighty", "Ninety"};

string helper(int num) {
string s;

if (num < 20)
s = belowTwenty.at(num);
else if (num < 100)
s = tens.at(num / 10) + " " + belowTwenty.at(num % 10);
else if (num < 1000)
s = helper(num / 100) + " Hundred " + helper(num % 100);
else if (num < 1000000)
s = helper(num / 1000) + " Thousand " + helper(num % 1000);
else if (num < 1000000000)
s = helper(num / 1000000) + " Million " + helper(num % 1000000);
else
s = helper(num / 1000000000) + " Billion " + helper(num % 1000000000);

trim(s);
return s;
}

void trim(string& s) {
s.erase(0, s.find_first_not_of(' '));
s.erase(s.find_last_not_of(' ') + 1);
}
};
``````

JAVA

``````class Solution {
public String numberToWords(int num) {
return num == 0 ? "Zero" : helper(num);
}

private final String[] belowTwenty = {"",        "One",     "Two",       "Three",    "Four",
"Five",    "Six",     "Seven",     "Eight",    "Nine",
"Ten",     "Eleven",  "Twelve",    "Thirteen", "Fourteen",
"Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"};
private final String[] tens = {"",      "",      "Twenty",  "Thirty", "Forty",
"Fifty", "Sixty", "Seventy", "Eighty", "Ninety"};

private String helper(int num) {
StringBuilder s = new StringBuilder();

if (num < 20)
s.append(belowTwenty[num]);
else if (num < 100)
s.append(tens[num / 10]).append(" ").append(belowTwenty[num % 10]);
else if (num < 1000)
s.append(helper(num / 100)).append(" Hundred ").append(helper(num % 100));
else if (num < 1000000)
s.append(helper(num / 1000)).append(" Thousand ").append(helper(num % 1000));
else if (num < 1000000000)
s.append(helper(num / 1000000)).append(" Million ").append(helper(num % 1000000));
else
s.append(helper(num / 1000000000)).append(" Billion ").append(helper(num % 1000000000));

return s.toString().trim();
}
}
``````

Python

``````class Solution:
def numberToWords(self, num: int) -> str:
if num == 0:
return "Zero"

belowTwenty = ["",        "One",       "Two",      "Three",
"Four",    "Five",      "Six",      "Seven",
"Eight",   "Nine",      "Ten",      "Eleven",
"Twelve",  "Thirteen",  "Fourteen", "Fifteen",
"Sixteen", "Seventeen", "Eighteen", "Nineteen"]
tens = ["",      "Ten",   "Twenty",  "Thirty", "Forty",
"Fifty", "Sixty", "Seventy", "Eighty", "Ninety"]

def helper(num: int) -> str:
if num < 20:
s = belowTwenty[num]
elif num < 100:
s = tens[num // 10] + " " + belowTwenty[num % 10]
elif num < 1000:
s = helper(num // 100) + " Hundred " + helper(num % 100)
elif num < 1000000:
s = helper(num // 1000) + " Thousand " + helper(num % 1000)
elif num < 1000000000:
s = helper(num // 1000000) + " Million " + \
helper(num % 1000000)
else:
s = helper(num // 1000000000) + " Billion " + \
helper(num % 1000000000)

return s.strip()

return helper(num)
``````