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LeetCode: Multiply Strings 解题报告

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.

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

 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032         while (ret.length() > 1 && ret.charAt(0) == ‘0‘) {33             ret.deleteCharAt(0);34         }35         36         return ret.toString();37     }38 }
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https://github.com/yuzhangcmu/LeetCode_algorithm/blob/master/string/Multiply.java

LeetCode: Multiply Strings 解题报告