Leetcode273 Integer to English Words

题目描述

Convert a non-negative integer to its English words representation. Given input is guaranteed to be less than 2的31 - 1.

Example 1:

1 2	Input: 123 Output: "One Hundred Twenty Three"

Example 2:

1 2	Input: 12345 Output: "Twelve Thousand Three Hundred Forty Five"

Example 3:

1 2	Input: 1234567 Output: "One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"

Example 4:

1 2	Input: 1234567891 Output: "One Billion Two Hundred Thirty Four Million Five Hundred Sixty Seven Thousand Eight Hundred Ninety One"

思路

建立三个数组，第一个string数组保存1-19的English string. 第二个数组保存20，30，40，50，60，70，80，90对应的English String.第三个数组保存hundred，thousand， million，billion，第四个数组中保存100，1000，100* 100， 1000* 1000

代码

class Solution {
    public String numberToWords(int num) {
        if(num==0) return "Zero";
        return convert(num).substring(0);
    }
    
    private static String convert(int num){
        String kUnder20[] = {"One", "Two", "Three", "Four", "Five", 
                               "Six", "Seven", "Eight", "Nine","Ten",
                               "Eleven", "Twelve", "Thirteen", "Fourteen",
                               "Fifteen", "Sixteen", "Seventeen", "Eighteen", 
                               "Nineteen"};
        String kUnder100[] = {"Twenty", "Thirty", "Forty", "Fifty", 
                                "Sixty", "Seventy", "Eighty", "Ninety"};
        String kHTMB[] = {"Hundred", "Thousand", "Million", "Billion"};
        int kP[] = {100, 1000, 1000*1000, 1000*1000*1000};
        if(num == 0) return "";
        if(num<20) {
            String result = kUnder20[num-1];
            return result;
        }
        if(num>=20&&num<100){
            String result = kUnder100[num/10-2];
            if(num%10>0)
                result = result +" ";
            return result+convert(num%10);
            
        }
        for(int i=3;i>=0;i--)
            if(num>=kP[i])
                return concat(convert(num/kP[i])+" "+ kHTMB[i],convert(num%kP[i]));
        return "";
    }
    private static String concat(String s1, String s2) {
        return s1 == "" ? s2 : s2 == "" ? s1 : s1 + " " + s2;
    }
}