【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