Multiply Strings

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.
  • Converting the input string to integer is NOT allowed.
  • You should NOT use internal library such as BigInteger.

 

思路：模拟乘法。数组记录。

 1 public class Solution {
 2     public String multiply(String num1, String num2) {
 3         if (num1 == null || num2 == null) {
 4             return null;
 5         }
 6         
 7         int len = num1.length() + num2.length();
 8         int i, j, product, carry;
 9         int[] num3 = new int[len];
10         for (i = num1.length() - 1; i >= 0; i--) {
11             carry = 0;
12             for (j = num2.length() - 1; j >= 0; j--) {
13                 product = carry + num3[i + j + 1] + Character.getNumericValue(num1.charAt(i)) * Character.getNumericValue(num2.charAt(j));
14                 num3[i + j + 1] = product % 10;
15                 carry = product / 10;
16             }
17             num3[i + j + 1] = carry;
18         }
19         i = 0;
20         while (i < len  && num3[i] == 0) {
21             i++;
22         }
23         StringBuilder sb = new StringBuilder();
24         if (i == len) {
25             sb.append(0);
26         }
27         while (i < len) {
28             sb.append(num3[i++]);
29         }
30         return sb.toString();
31         
32     }
33 }

 

posted @ 2016-06-07 09:23  YuriFLAG  阅读(123)  评论(0)    收藏  举报