Multiply Strings

 1 class Solution {
 2 public:
 3     string multiply(string num1, string num2) {
 4         int l1 = num1.length();
 5         int l2 = num2.length();
 6         int l3 = l1+l2;
 7         int result[l1+l2];
 8         memset(result,0,sizeof(result));
 9         int carryer = 0;
10         int t = 0;
11         for ( int i = 0; i < l1; i++ ) {
12             carryer = 0;
13             for ( int j = 0; j < l2; j++ ) {
14                 t = (num1[l1-1-i]-'0')*(num2[l2-1-j]-'0')+carryer+result[l3-1-i-j];
15                 result[l3-1-i-j] = t%10;
16                 carryer = t/10;
17             }
18             result[l3-1-i-l2] += carryer;
19         }
20         string re = "";
21         char ch;
22         int i = 0;
23         while ( i < l3 && result[i] == 0 ) {
24             i++;
25         }
26         if ( i == l3 ) {
27             return "0";
28         }
29         for ( ; i < l3; i++ ) {
30             ch = '0'+result[i];
31             re += ch;
32         }
33         return re;
34     }
35 };