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LeetCode: Multiply Strings 解题报告

时间:2014-11-23 11:39:36      阅读:224      评论:0      收藏:0      [点我收藏+]

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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.

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SOLUTION 1:

参考自http://blog.csdn.net/fightforyourdream/article/details/17370495

相当优雅的算法,主页君稍微改进,把翻转String这一步拿掉了。比起一般的做法,这个算法很容易就BUG FREE.

思路:
1 建立数组,双层循环遍历两个string,把单位的乘积累加到数组相应的位置
2 处理进位并输出
3 注意前导零的corner case

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 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 len1 = num1.length();
 8         int len2 = num2.length();
 9         
10         int[] product = new int[len1 + len2];
11         
12         // 计算相应位置的product.
13         for (int i = 0; i < len1; i++) {
14             for (int j = 0; j < len2; j++) {
15                 // 注意,这里要使用+=以不断累加乘积
16                 product[i + j] += (num1.charAt(len1 - 1 - i) - ‘0‘) * (num2.charAt(len2 - 1 - j) - ‘0‘);
17             }
18         }
19         
20         StringBuilder ret = new StringBuilder();
21         
22         int carry = 0;
23         // 计算进位
24         for (int i = 0; i < len1 + len2; i++) {
25             product[i] = product[i] + carry;
26             int digit = product[i] % 10;
27             carry = product[i] / 10;
28             ret.insert(0, digit);
29         }
30         
31         // 去掉前导0
32         while (ret.length() > 1 && ret.charAt(0) == ‘0‘) {
33             ret.deleteCharAt(0);
34         }
35         
36         return ret.toString();
37     }
38 }
View Code

 

请至主页群GITHUB:

https://github.com/yuzhangcmu/LeetCode_algorithm/blob/master/string/Multiply.java

LeetCode: Multiply Strings 解题报告

标签:style   blog   http   io   ar   color   os   使用   sp   

原文地址:http://www.cnblogs.com/yuzhangcmu/p/4116211.html

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