python leetcode 字符串相乘实例详解

class Solution:
  def multiply(self, num1, num2):
    """
    :type num1: str
    :type num2: str
    :rtype: str
    """
    return str(eval(num1+'*'+num2))

class Solution:
  def multiply(self, num1, num2):
    """
    :type num1: str
    :type num2: str
    :rtype: str
    """
    dict = {'0':0, '1':1, '2':2, '3':3, '4':4, '5':5, '6':6, '7':7, '8':8, '9':9}
    if (num1=='0' or num2=='0'):
      return "0"
    n1 = 0
    n2 = 0
    for c in num1:
      val = dict[c]
      n1 = n1*10 + val
    for s in num2:
      val = dict[s]
      n2 = n2*10 + val
    result = n1 * n2;
    return str(result)

class Solution(object):
  def multiply(self, num1, num2):
    """
    :type num1: str
    :type num2: str
    :rtype: str
    """
    if num1 == "0" or num2 == "0":
      return "0"
    num1 = num1[::-1]
    num2 = num2[::-1]
    str_list = [0 for _ in range(len(num1)+len(num2))]
    for i in range(len(num1)):
      for j in range(len(num2)):
        str_list[i+j] += (int(num1[i])*int(num2[j]))
    result = ""
    up = 0
    for i in str_list:
      now = i + up
      cur = now % 10
      up = now / 10
      result += str(cur)
    begin = 0
    result = result[::-1]
    for i in result:
      if i == "0":
        begin += 1
      else:
        break
    return result[begin:]