leetcode - 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.

class Solution {
public:
    std::string multiply(std::string num1, std::string num2) {
		if(num1 == "0" || num2 == "0") return "0";
		int l1 = num1.size(),l2 = num2.size();
		std::vector
  
    vec1(l1,0);
		std::vector
   
     vec2(l2,0); std::vector
    
      res(l1+l2,0); for (int i = 0; i < l1; i++) { vec1[i] = num1[i] - '0'; } for (int i = 0; i < l2; i++) { vec2[i] = num2[i] - '0'; } for (int i = 0; i < l1; i++) { for (int j = 0; j < l2; j++) { res[i+j+1] += vec1[i] * vec2[j]; } } std::string s; for(int i = l1 + l2 - 1; i >= 0; i--) { if(res[i] > 0) res[i-1] += res[i] / 10; res[i] %= 10; s = (char)(res[i] + '0') + s; } return s[0] == '0' ? s.substr(1) : s; } };