273 Integer to English Words

Leetcode

Convert a non-negative integer num to its English words representation.

Example 1:

Input: num = 123
Output: "One Hundred Twenty Three"

Example 2:

Input: num = 12345
Output: "Twelve Thousand Three Hundred Forty Five"

Example 3:

Input: num = 1234567
Output: "One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven"

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解法如下。尝试了 10 次才成功。。。

class Solution {
    String[] IN_TEN = {
        "","One","Two","Three","Four","Five","Six","Seven","Eight","Nine","Ten"
    };

    String[] IN_TWENTY = {
        "Eleven","Twelve","Thirteen","Fourteen","Fifteen",
        "Sixteen","Seventeen","Eighteen","Nineteen","Twenty"
    };

    String[] IN_HUNDRED = {
        "Twenty","Thirty","Forty","Fifty","Sixty","Seventy","Eighty","Ninety"
    };
    
    public String numberToWords(int num) {
        if(num==0) return "Zero";
        return helper(num).trim();
    }
    
    private String helper(int num){
        
        if(num==0) return "";
        
        if(num<=10) return IN_TEN[num];
        
        if(num<=20) return IN_TWENTY[num-11];
        
        if(num<100) {
            int i1 = num/10;
            int i2 = num%10;
            if(i2==0) return IN_HUNDRED[i1-2];
            return IN_HUNDRED[i1-2]+ " " + IN_TEN[i2];
        }
        
        if(num<1000){
            int i1 = num/100;
            int i2 = num%100;
            if(i2==0) return IN_TEN[i1] + " Hundred";
            return IN_TEN[i1] + " Hundred " + helper(i2);
        }
        
        if(num<1_000_000){
            int i1=num/1000;
            int i2=num%1000;
            if(i2==0) return helper(i1)+" Thousand";
            return helper(i1)+" Thousand "+helper(i2);
        }
        
        if(num<1_000_000_000){
            int i1=num/1_000_000;
            int i2=num%1_000_000;
            if(i2==0) return helper(i1)+" Million";
            return helper(i1)+" Million "+helper(i2);
        } 
        
        int i1=num/1_000_000_000;
        int i2=num%1_000_000_000;
        if(i2==0) return helper(i1)+" Billion";
        return helper(i1)+" Billion "+helper(i2);

    }
}