[Leetcode][python]Multiply Strings/字符串相乘

123*456

100        400
 20         50
  3          6

[3*6, 2*6+3*5, 1*6+2*5+3*4, 2*4+1*5, 1*4, 0]

[18, 27, 28, 13, 4, 0]

[8, 27+1, 28, 13, 4, 0]

[8, 8, 28+2, 13, 4, 0]

[8, 8, 0, 13+3, 4, 0]

[8, 8, 0, 6, 5, 0]

"880650"-->"056088"

"56088"

class Solution(object):
    def multiply(self, num1, num2):
        """
        :type num1: str
        :type num2: str
        :rtype: str
        """
        num1 = num1[::-1]
        num2 = num2[::-1]
        length1 = len(num1)
        length2 = len(num2)
        temp = [0 for __ in range(length1 + length2)]  # 最多是length1 + length2位数
        # 将手算乘法的每列数字放入其格内
        for i in range(len(num1)):
            for j in range(len(num2)):
                # temp[i+j]是重点
                temp[i+j] += int(num1[i]) * int(num2[j])
        print temp

        ans = []
        for i in range(len(temp)):
            digit = temp[i] % 10  # 该位最后的数
            carry = temp[i] / 10  # 进位的数
            if i < len(temp)-1:
                temp[i+1] += carry
            ans.insert(0, str(digit))  # 直接往前写，省的最后反转
        # 删去前面的所有0
        while ans[0] == '0' and len(ans) > 1:
            ans.pop(0)
        return ''.join(ans)