Straight forward idea. Just like the way we multiply numbers. Don't forget considering the carry and be careful. e.g.

  123*456,

what we usually do is:

      123

*    456

-----------

      738

    615

+492

-----------

  56088

thus, 123*456 = 56088.

In the same way, the algorithm is:

from end to start position, use a new array to store temproary digit.

A*B

(1)For each element B[i]

    Compute tmp = B[i]*A

    Add tmp to the previous result, note the start position. res = res"+"tmp

(2)Return result.

To be specific,

(1) char2int,     int(char-'0');

(2) int2char,     char(int+'0')

(3) Don't forget the carry in each add or multiply operation.

(4) Don't forget the carry after last operation. e.g.  82+33 = 115.

(5) Be careful with the string order and the number order.

public class Solution {    public String multiply(String num1, String num2) {        //用字符串模拟乘法，注意事项见上面分析。注意result的第0位是结果的个位                int len1=num1.length();        int len2=num2.length();        int[] result=new int[len1+len2];        int carry=0;        int i=0;        int j=0;        for( i=0;i
     
      0){            if(result[i]!=0)                break;            i--;        }        StringBuilder res=new StringBuilder();        int k=i;        while(k>=0){            res.append((char)(result[k]+'0'));//res.append(result[k]+'0');会得整数，比如result[k]为0时，添加的是48            k--;        }                return res.toString();    }}