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| class Solution {
public String numberToWords(int num) {
String str = String.valueOf(num);
String firstPart = null, midPart = null;
String lastPart = str.substring(Math.max(0, str.length() - 3));
if (str.length() > 3) {
midPart = str.substring(Math.max(0, str.length() - 6), str.length() - 3);
}
if (str.length() > 6) {
firstPart = str.substring(0, str.length() - 6);
}
List<String> wordList = new ArrayList<>();
if (firstPart != null) {
List<String> firstWordList = toWordList(firstPart);
if (!firstWordList.isEmpty()) {
wordList.addAll(firstWordList);
if (!firstWordList.get(firstWordList.size() - 1).equals("Billion")) {
wordList.add("Million");
}
}
}
if (midPart != null) {
List<String> midWordList = toWordList(midPart);
if (!midWordList.isEmpty()) {
wordList.addAll(midWordList);
wordList.add("Thousand");
}
}
wordList.addAll(toWordList(lastPart));
return String.join(" ", wordList);
}
private List<String> toWordList(String part) {
if (part.length() == 1) {
return Collections.singletonList(charToWord(part.charAt(0)));
} else if (part.length() == 2) {
return twoCharToWord(part.charAt(0), part.charAt(1));
} else if (part.length() == 3) {
List<String> wordList = new ArrayList<>();
char c1 = part.charAt(0);
if (c1 != '0') {
wordList.add(charToWord(part.charAt(0)));
wordList.add("Hundred");
}
wordList.addAll(twoCharToWord(part.charAt(1), part.charAt(2)));
return wordList;
} else if (part.length() == 4) {
List<String> wordList = new ArrayList<>();
wordList.add(charToWord(part.charAt(0)));
wordList.add("Billion");
char c1 = part.charAt(1);
if (c1 != '0') {
wordList.add(charToWord(part.charAt(1)));
wordList.add("Hundred");
}
wordList.addAll(twoCharToWord(part.charAt(2), part.charAt(3)));
return wordList;
} else {
throw new IllegalArgumentException("Unsupported part: " + part);
}
}
private List<String> twoCharToWord(char c1, char c2) {
if (c1 == '0' && c2 == '0') {
return Collections.emptyList();
}
if (c1 == '0') {
return Collections.singletonList(charToWord(c2));
} else if (c1 == '1') {
switch (c2) {
case '0':
return Collections.singletonList("Ten");
case '1':
return Collections.singletonList("Eleven");
case '2':
return Collections.singletonList("Twelve");
case '3':
return Collections.singletonList("Thirteen");
case '4':
return Collections.singletonList("Fourteen");
case '5':
return Collections.singletonList("Fifteen");
case '6':
return Collections.singletonList("Sixteen");
case '7':
return Collections.singletonList("Seventeen");
case '8':
return Collections.singletonList("Eighteen");
case '9':
return Collections.singletonList("Nineteen");
default:
throw new IllegalArgumentException("Unsupported char: " + c2);
}
} else {
List<String> wordList = new ArrayList<>(2);
switch (c1) {
case '2':
wordList.add("Twenty");
break;
case '3':
wordList.add("Thirty");
break;
case '4':
wordList.add("Forty");
break;
case '5':
wordList.add("Fifty");
break;
case '6':
wordList.add("Sixty");
break;
case '7':
wordList.add("Seventy");
break;
case '8':
wordList.add("Eighty");
break;
case '9':
wordList.add("Ninety");
break;
default:
throw new IllegalArgumentException("Unsupported char: " + c2);
}
if (c2 != '0') {
wordList.add(charToWord(c2));
}
return wordList;
}
}
private String charToWord(char c) {
switch (c) {
case '0':
return "Zero";
case '1':
return "One";
case '2':
return "Two";
case '3':
return "Three";
case '4':
return "Four";
case '5':
return "Five";
case '6':
return "Six";
case '7':
return "Seven";
case '8':
return "Eight";
case '9':
return "Nine";
default:
throw new IllegalArgumentException("Unsupported char: " + c);
}
}
}
|
References
273. Integer to English Words
面试题 16.08. 整数的英语表示