【LeetCode】Multiply Strings

Multiply Strings 
Total Accepted: 9184 Total Submissions: 45371 My Submissions
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.
【解题思路】
1、数学计算的基本思想转为代码实现。
2、num1和num2按位相乘，累加。
3、两数相乘最大位数，是len(num1)+len(num2)
4、注意两者之中出现"000"这种情况的返回值
5、比较考验基本功底，建议练习。

Java AC 476ms

public class Solution {    public String multiply(String num1, String num2) {if ("".equals(num1.replace("0", ""))|| "".equals(num2.replace("0", ""))) {return "0";}int len1 = num1.length();int len2 = num2.length();char arrayA[];char arrayB[];arrayA = num1.toCharArray();arrayB = num2.toCharArray();int column = len1 + len2;int array[] = new int[column];int k = column;for (int i = len2 - 1; i >= 0; i--) {k--;int tempCol = k;int tempArr[] = new int[column];int num = arrayB[i] - '0';for (int j = len1 - 1; j >= 0; j--) {tempArr[tempCol] += (arrayA[j] - '0') * num;if (tempArr[tempCol] >= 10) {int mod = tempArr[tempCol] / 10;tempArr[tempCol] %= 10;tempArr[tempCol - 1] += mod;}tempCol--;}array = addNum(tempArr, array, column);}StringBuffer sb = new StringBuffer();int i = 0;if (array[0] == 0) {i = 1;}for (; i < column; i++) {sb.append(array[i]);}return sb.toString();}public int[] addNum(int tempArr[], int array[], int column) {for (int i = column - 1; i >= 0; i--) {array[i] += tempArr[i];if (array[i] >= 10) {array[i] -= 10;array[i - 1] += 1;}}return array;}}

Python AC 944ms

class Solution:    # @param num1, a string    # @param num2, a string    # @return a string    def multiply(self, num1, num2):        if int(num1) == 0 or int(num2) == 0:            return '0'        len1 = len(num1)        len2 = len(num2)        col = len1 + len2        list = [0 for i in range(col)]        list1 = [int(num1[i]) for i in range(len1)]        list2 = [int(num2[i]) for i in range(len2)]        k = col        for i in range(len2-1, -1, -1):            k -= 1            tempCol = k            tempList = [0 for l in range(col)]            for j in range(len1-1, -1, -1):                tempList[tempCol] += list1[j] * list2[i]                if tempList[tempCol] >= 10 :                    mod = tempList[tempCol] / 10                    tempList[tempCol] %= 10                    tempList[tempCol - 1] += mod                tempCol -= 1            list = self.addNum(tempList, list, col)        if list[0] == 0:            list = list[1:]        list = [str(e) for e in list]        return "".join(list)    def addNum(self, tempList, list, col):        for i in range(col-1, -1, -1):            list[i] += tempList[i]            if(list[i] >= 10):                list[i] -= 10                list[i-1] += 1        return list