LeetCode 273.Integer to English Words【Java】

Title description

Integer to English Words

AC code

The meaning of this question is to give you a number so that you can express the corresponding English reading. Reading a number in English has a characteristic that every three numbers are a group (you can observe the sample reading given). That we can represent a number: the range wherein the array is underlined 1 to 999 (the last underline, this number 0 Laid separate out sentence), __million__billion__thousand___. You can write a part function separately for each underlined part, that is to say, enter a number within 1000, the part method can return its corresponding English reading, and finally each part is spliced ​​on the corresponding million / billion / thousand .

class Solution {
    String[] small={"Zero","One","Two","Three","Four","Five","Six","Seven","Eight","Nine","Ten",
        "Eleven","Twelve","Thirteen","Fourteen","Fifteen","Sixteen","Seventeen","Eighteen","Nineteen"};
    String[] decade={"","","Twenty","Thirty","Forty","Fifty","Sixty","Seventy","Eighty","Ninety"};
    String[] big={"Billion","Million","Thousand",""};
    public String numberToWords(int num) {
    	//特判0。
        if(num==0) return small[0];
        String res="";
        for(int i=1000000000,j=0;i>0;i/=1000,j++)
        {
            if(num>=i){
                res+=part(num/i)+big[j]+' ';
                num%=i;
            }
        }
        while(res.charAt(res.length()-1)==' ') res=res.substring(0,res.length()-1);
        return res;
    }

    String part(int num){
        String res="";
        if(num>=100){
            //此处需要注意Hundred前后都有空格
            res+=small[num/100]+" Hundred ";
            num%=100;
        }
        if(num==0) return res;
        //小于20的，可以直接加
        if(num>=20){
            res+=decade[num/10]+' ';
            num%=10;
        }
        if(num==0) return res;
        res+=small[num]+' ';
        return res;
    }
}