Leetcode 43. Multiply Strings

 1 class Solution {
 2 public:
 3     string multiply(string num1, string num2) {
 4         int i = 0, j;
 5         //去除头0
 6         while (i < num1.size() && num1[i] == ‘0‘) i++;
 7         if (i == num1.size()) return "0";
 8         num1 = num1.substr(i);
 9         i = 0;
10         while (i < num2.size() && num2[i] == ‘0‘) i++;
11         if (i == num2.size()) return "0";
12         num2 = num2.substr(i);
13         vector<int> nums(num1.size()+num2.size(),0);
14         for (i = num1.size() - 1; i >= 0; i--) {
15             for (j = num2.size() - 1; j >= 0; j--) {
16                 int mutil = (num1[i]-‘0‘)*(num2[j]-‘0‘) + nums[i + j + 1];
17                 nums[i + j + 1] = mutil % 10;
18                 nums[i + j] += mutil / 10;//这个可以保证不会溢出
19             }
20         }
21         string res = "";
22         j = 0;
23         while (nums[j] == 0) j++;
24         while (j < nums.size()) res += to_string(nums[j++]);
25         return res;
26     }
27 };