【leetcode】Multiply Strings

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.

 

 

各个位相乘，保存在数组中，最后再处理进位。

如

123*456

 

  4,5,6

     8,10,12

        12,15,18

________________

   4,13,28,27,18

 

即56088

 

 1 class Solution {

 2 public:

 3     string multiply(string num1, string num2) {

 4        

 5         if(num1=="0"||num2=="0") return "0";

 6        

 7         while(num1[0]=='0') num1.erase(0);

 8         while(num2[0]=='0') num2.erase(0);

 9        

10         int n1=num1.size();

11         int n2=num2.size();

12        

13         int *numArr1=new int[n1];

14         int *numArr2=new int[n2];

15        

16         int *result=new int[n1+n2];

17         memset(result,0,sizeof(int)*(n1+n2));

18         for(int i=0;i<n1;i++) numArr1[i]=num1[i]-'0';

19         for(int i=0;i<n2;i++) numArr2[i]=num2[i]-'0';

20        

21         for(int i=0;i<n1;i++)

22         {

23             for(int j=0;j<n2;j++)

24             {

25                 result[i+j+1]+=numArr1[i]*numArr2[j];

26             }

27         }

28        

29         int carry=0;

30         for(int i=n1+n2-1;i>=0;i--)

31         {

32             result[i]+=carry;

33             if(result[i]>=10)

34             {

35                 carry=result[i]/10;

36                 result[i]=result[i]%10;

37             }

38             else

39             {

40                 carry=0;

41             }

42         }

43        

44         string resultStr;

45         int k=0;

46         while(result[k]==0) k++;

47        

48         for(int i=k;i<n1+n2;i++)

49         {

50             resultStr.push_back(result[i]+'0');

51         }

52        

53         return resultStr;

54     }

55 };