Multiply Strings

Problem:

Given two numbers represented as strings, return multiplication of the numbers as a string.

Note: The numbers can be arbitrarily large and are non-negative.

Analysis:
Step 1: Convert string to integer arrays. Note that the int of the char is acquired by char-'0'.
Step 2: Multiply the integer arrays into a combined one. res[i+j+1]+=n1[i]+n2[j].
Step 3: Convert array back to string.

LeetCode说我test case "0","0"没通过，明明在Eclipse通过了的，答案就""。不管了。

Solution:

1:  public static String multiplyString(String num1, String num2)  
2:       {                      
3:            if(num1.isEmpty()||num2.isEmpty()||num1=="0"||num2=="0")  
4:                 return "0";  
5:            int l1=num1.length();  
6:            int l2=num2.length();  
7:            int[] n1=new int[l1];  
8:            int[] n2=new int[l2];  
9:            int[] res=new int[l1+l2];  
10:            //Convert string to integer arrays. Note that the int of the char is acquired by char-'0'.  
11:            for(int i = 0;i<l1;i++)  
12:            {  
13:                 n1[i]=num1.charAt(i)-'0';  
14:            }  
15:            for(int i=0;i<l2;i++)  
16:            {  
17:                 n2[i]=num2.charAt(i)-'0';  
18:            }  
19:            //Multiply the integer arrays into a combined one.  
20:            for(int i=0;i<l1;i++)  
21:                 for(int j=0;j<l2;j++)  
22:                 {  
23:                      res[i+j+1]+=n1[i]*n2[j];  
24:                 }  
25:            //Convert array back to string  
26:            StringBuilder sb= new StringBuilder();  
27:            for(int i=0;i<l1+l2;i++)  
28:            {  
29:                 if(res[i]!=0)  
30:                      sb.append(res[i]);  
31:            }  
32:            return sb.toString();  
33:        }