LeetCode Online Judge 题目C# 练习 - 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.

 1         public static string MultiplyStrings(string num1, string num2)

 2         {

 3             if (num1.Length == 0 || num2.Length == 0)

 4                 return "0";

 5 

 6             int carry = 0;

 7             List<int> l1 = new List<int>();

 8             List<int> l2 = new List<int>();

 9             for (int i = num2.Length - 1; i >= 0; i--)

10             {

11                 List<int> curr;

12                 if (l1.Count == 0)

13                     curr = l1;

14                 else

15                 {

16                     curr = l2;

17                     //Adding 0 to the end

18                     for (int k = i; k < num2.Length - 1; k++)

19                     {

20                         curr.Add(0);

21                     }

22                 }

23 

24                 for (int j = num1.Length - 1; j >= 0; j--)

25                 {

26                     int b = num2[i] - '0';

27                     int a = num1[j] - '0';

28                                         

29                     curr.Add(((a * b) % 10 + carry) % 10);

30                     carry = (a * b + carry) / 10;

31                 }

32 

33                 if (carry > 0)

34                     curr.Add(carry);

35 

36                 carry = 0;

37 

38                 //Adding l1 and l2 into l1;

39                 if (l2.Count > 0)

40                 {

41                     int k = 0;

42                     while (k < l1.Count || k < l2.Count)

43                     {

44                         int a = k < l1.Count ? l1[k] : 0;

45                         int b = k < l2.Count ? l2[k] : 0;

46 

47                         if (k < l1.Count)

48                             l1[k] = ((a + b + carry) % 10);

49                         else

50                             l1.Add((a + b + carry) % 10);

51                         carry = (a + b + carry) / 10;

52 

53                         k++;

54                     }

55 

56                     if (carry > 0)

57                         l1.Add(carry);

58 

59                     carry = 0;

60                 }

61                 l2.Clear();

62             }

63 

64             string ret = "";

65             for (int i = l1.Count - 1; i >= 0; i--)

66             {

67                 if (l1[i] != 0 || ret != "")

68                     ret = ret + l1[i].ToString();

69             }

70 

71             return ret == "" ? "0" : ret; ;

72         }

代码分析：

　　也是没有技巧的题目，细心注意输出的结果就行。