LeetCode: Integer to English Words

LeetCode: 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,

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

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public class Solution {
private static final Map<Integer, String> intMap = new HashMap<>();
private static final List<String> list = new ArrayList<>();

static {
intMap.put(0, "Zero");
intMap.put(1, "One");
intMap.put(2, "Two");
intMap.put(3, "Three");
intMap.put(4, "Four");
intMap.put(5, "Five");
intMap.put(6, "Six");
intMap.put(7, "Seven");
intMap.put(8, "Eight");
intMap.put(9, "Nine");
intMap.put(10, "Ten");
intMap.put(11, "Eleven");
intMap.put(12, "Twelve");
intMap.put(13, "Thirteen");
intMap.put(14, "Fourteen");
intMap.put(15, "Fifteen");
intMap.put(16, "Sixteen");
intMap.put(17, "Seventeen");
intMap.put(18, "Eighteen");
intMap.put(19, "Nineteen");
intMap.put(20, "Twenty");
intMap.put(30, "Thirty");
intMap.put(40, "Forty");
intMap.put(50, "Fifty");
intMap.put(60, "Sixty");
intMap.put(70, "Seventy");
intMap.put(80, "Eighty");
intMap.put(90, "Ninety");

list.add("");
list.add("Thousand");
list.add("Million");
list.add("Billion");
}

public String numberToWords(int num) {
StringBuilder sb = new StringBuilder();
int index = 0;
while (num > 0) {
int n = num % 1000;
sb.insert(0, toStr(n, index));
num = num / 1000;
index++;
}

return sb.length() == 0 ? "Zero" : sb.toString().replace(" "," ").trim();
}

// num < 1000
private String toStr(int num, int index) {
if (num == 0) {
return "";
}

StringBuilder sb = new StringBuilder();
int n = num / 100;
if (n > 0) {
sb.append(intMap.get(n)).append(" Hundred ");
}

num = num % 100;
n = num / 10;
if (n == 1) {
sb.append(intMap.get(num));
} else {
if (n != 0) {
sb.append(intMap.get(n * 10));
}
n = num % 10;
if (n != 0) {
sb.append(" ").append(intMap.get(n));
}
}

sb.append(" ").append(list.get(index)).append(" ");
return sb.toString();
}
}