Multiply Strings.java

public class Solution {
    public String multiply(String num1, String num2) {
        // Start typing your Java solution below
        // DO NOT write main() function
        if(num1.compareTo("0")==0 || num2.compareTo("0")==0 ) return "0";
        int length1=num1.length(); int length2=num2.length(); 
        int [] array=new int [length1+length2];
        int carry=0; 
        for(int i=length1-1; i>=0; i--)
        {
            for(int j=length2-1; j>=0; j--)
            {
                int temp=array[length1+length2-2-i-j]; 
                temp+=(num1.charAt(i)-'0')*(num2.charAt(j)-'0')+carry; 
                if(temp>=10)
                {
                    carry=temp/10; temp%=10; 
                }else carry=0; 
                array[length1+length2-2-i-j]=temp;
            }
            if(carry!=0)
            {
                array[length1+length2-i-1]=carry; carry=0; 
            }
        }
        StringBuffer sb=new StringBuffer(); 
        if(array[length1+length2-1]!=0) sb.append(array[length1+length2-1]);
        for(int i=length1+length2-2; i>=0; i--)
        {
            sb.append(array[i]);
        }
        return sb.toString(); 
    }
}