05 August 2008
Convert a non-negative integer to its english words representation. Given input is guaranteed to be less than 231 - 1.
Example 1:
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Input: 123
Output: "One Hundred Twenty Three"
Example 2:
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Input: 12345
Output: "Twelve Thousand Three Hundred Forty Five"
Example 3:
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Input: 1234567
Output: "One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"
Example 4:
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Input: 1234567891
Output: "One Billion Two Hundred Thirty Four Million Five Hundred Sixty Seven Thousand Eight Hundred Ninety One"
要求把整数转换成英文单词，利用数组来枚举， 3个一组的进行处理，而且题目中限定了输入数字范围为0到2^31 - 1之间，最高只能到billion位，3个一组也只需处理四组即可，那么我们需要些一个处理三个一组数字的函数。
需要把1到19的英文单词都列出来，放到一个数组里，还要把20,30，… 到90的英文单词列出来放到另一个数组里，然后需要用写技巧，比如一个三位数n，百位数表示为n/100，后两位数一起表示为n%100，十位数表示为n%100/10，个位数表示为n%10，然后我们看后两位数是否小于20，小于的话直接从数组中取出单词，如果大于等于20的话，则分别将十位和个位数字的单词从两个数组中取出来。然后再来处理百位上的数字，还要记得加上Hundred。主函数中调用四次这个帮助函数，然后中间要插入”Thousand”, “Million”, “Billion”到对应的位置，最后check一下末尾是否有空格，把空格都删掉，返回的时候检查下输入是否为0，是的话要返回’Zero’。
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class Solution {
private final String[] LESS_THAN_20 = {"", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen", "Sixteen", "Seventeen", "Eighteen", "Nineteen"};
private final String[] TENS = {"", "Ten", "Twenty", "Thirty", "Forty", "Fifty", "Sixty", "Seventy", "Eighty", "Ninety"};
private final String[] HUNDREDS = {"", "One", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine"};
private final String[] THOUSANDS = {"", "Thousand", "Million", "Billion"};
public String numberToWords(int num) {
if (num == 0) {
return "Zero";
}
int i = 0;
String words = "";
while (num > 0) {
if (num % 1000 != 0) {
words = numberToWordsHelper(num % 1000) + THOUSANDS[i] + " " + words;
}
num /= 1000;
i++;//指针每次在THOUSANDS数组里面挪动读取对应的字母
}
return words.trim();
}
private String numberToWordsHelper(int num) {
if (num == 0) {
return "";
} else if (num < 20) {
return LESS_THAN_20[num] + " ";
} else if (num < 100) {
return TENS[num / 10] + " " + numberToWordsHelper(num % 10);
} else {
return HUNDREDS[num / 100] + " Hundred " + numberToWordsHelper(num % 100);
}
}
}