LeetCode -- Integer to English Words

public class Solution {
    
    public string NumberToWords(int num) 
    {
        if(num == 0){
    		return "Zero";
    	}
	
    	var str = num.ToString();
    	
    	if(num > 999999999){
    		var s1 = str.Substring(0,str.Length - 9);
    		var n1 = int.Parse(s1);
    		var s2 = str.Substring(str.Length - 9, 9);
    		
    		var s = Millions(s1) + " Billion " + Millions(s2);
    		s = s.TrimEnd();
    		return s;
    	}
    	else{
    		return Millions(str);
    	}
    }
    
    private string Millions(string str)
    {
    	var n = int.Parse(str);
    	if(n > 999999){
    		var s1 = str.Substring(0,str.Length - 6);
    		var n1 = int.Parse(s1);
    		var s2 = str.Substring(str.Length - 6, 6);
    		
    		var s = Thousands(s1) + " Million " + Thousands(s2);
    		s = s.TrimEnd();
    		return s;
    	}
    	else{
    		return Thousands(n.ToString());
    	}
    }
    
    
    private string Thousands(string str)
    {
    	var n = int.Parse(str);
    	if(n > 999){
    		var s1 = str.Substring(0,str.Length - 3);
    		var n1 = int.Parse(s1);
    		var s2 = str.Substring(str.Length - 3, 3);
    		
    		var s = Hundreds(s1)+ " Thousand " + Hundreds(s2);
    		s = s.TrimEnd();
    		return s;
    	}
    	else{
    		return Hundreds(n.ToString());
    	}
    }
    
    private string Hundreds(string str)
    {
    	int n = int.Parse(str);
    	if(n < 10){
    		return Digit(str.Last());
    	}
    	else if(n == 10){
    		return "Ten";
    	}
    	else if(n > 10 && n < 20)
    	{
    		return Teen(str.Substring(str.Length - 2,2));
    	}
    	else if(n >= 20 && n < 100)
    	{
    		return Ty(str.Substring(str.Length - 2,2));
    	}
    	else if(n >= 100 && n <= 999)
    	{
    		var c1 = str[0];
    		var s = Digit(c1) + " Hundred";
    		
    		var c2 = str[1];
    		var c3 = str[2];
    		if(c2 == ‘0‘){
    			return c3 != ‘0‘ ? s + " " + Digit(c3) : s;	
    		}
    		if(c2 == ‘1‘){
    			return s + " " + Teen(str.Substring(str.Length - 2,2));
    		}
    		else{
    			return s + " " + Ty(str.Substring(str.Length - 2,2));
    		}
    	}
    	else{
    		throw new ArgumentException("input should be less than 1000");
    	}
    }
    
    private string Teen(string str)
    {
    	switch(str){
    		case "10":
    		return "Ten";
    		case "11":
    		return "Eleven";
    		case "12":
    		return "Twelve";
    		case "13":
    		return "Thirteen";
    		case "14":
    		return "Fourteen";
    		case "15":
    		return "Fifteen";
    		case "16":
    		return "Sixteen";
    		case "17":
    		return "Seventeen";
    		case "18":
    		return "Eighteen";
    		case "19":
    		return "Nineteen";
    		default :
    		throw new ArgumentException("input should be from 11 to 19 ONLY.");
    	}
    }
    
    private string Ty(string str)
    {
    	var c1 = str[0];
    	var c2 = str[1];
    	var space = c2 == ‘0‘ ? "" : " ";
    	switch(c1){
    		case ‘2‘:
    		return "Twenty" +space+ Digit(c2);
    		case ‘3‘:
    		return "Thirty" +space+ Digit(c2);
    		case ‘4‘:
    		return "Forty" +space+ Digit(c2);
    		case ‘5‘:
    		return "Fifty" +space+ Digit(c2);
    		case ‘6‘:
    		return "Sixty" +space+ Digit(c2);
    		case ‘7‘:
    		return "Seventy" +space+ Digit(c2);
    		case ‘8‘:
    		return "Eighty" +space+ Digit(c2);
    		case ‘9‘:
    		return "Ninety" +space+ Digit(c2);
    		default :
    		throw new ArgumentException(string.Format("input should between [20,99], but got {0}",c1));
    	}
    }
    
    private string Digit(char c)
    {
    	switch(c){
    		case ‘0‘:
    		return "";
    		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 ArgumentException("input should beteen [0-9]");
    	}
    }


}

LeetCode -- Integer to English Words

原文：http://blog.csdn.net/lan_liang/article/details/49885299