代码：
1 #include<iostream> 2 #include<string> 3 #include<vector> 4 5 using namespace std; 6 7 void swap(char &a, char &b) 8 { 9 char c = a; 10 a = b; 11 b = c; 12 } 13 14 void reverse(string &s) 15 { 16 int L = s.size(); 17 int i = 0; 18 while (i <= (L-1) / 2) 19 { 20 swap(s[i], s[L - i-1]); 21 i++; 22 } 23 } 24 25 string multiply(string num1, string num2) 26 { 27 if (num1 == "0" || num2 == "0") 28 return "0"; 29 int L1 = num1.length(); 30 int L2 = num2.length(); 31 reverse(num1); 32 reverse(num2); 33 int *result = new int[L1+L2]; 34 memset(result, 0, (L1 + L2)*sizeof(int)); 35 int i, j; 36 int c; 37 for (i = 0; i <L1; i++) 38 { 39 c = 0; 40 for (j = 0; j <L2; j++) 41 { 42 int mul = (num1[i]-'0') *( num2[j]-'0'); 43 int cur = mul % 10 + c + result[i + j]; 44 result[i + j] = cur % 10; 45 c = cur / 10 + mul / 10; 46 } 47 if (c>0) 48 result[i + j] += c; 49 } 50 string resultS = ""; 51 if (result[L1 + L2 -1] != 0) 52 resultS += (result[L1 + L2-1] + '0'); 53 for (int i = L1 + L2-2; i >=0; i--) 54 resultS += (result[i] + '0'); 55 return resultS; 56 } 57 58 int main() 59 { 60 cout<<multiply("9", "9")<<endl; 61 return 0; 62 }
