Multiply Strings | Leetcode 43 solution

 Multiply Strings Leetcode solution 

Given two non-negative integers num1 and num2 represented as strings, return the product of num1 and num2, also represented as a string.

Note: You must not use any built-in BigInteger library or convert the inputs to integer directly.

 

Example 1:

Input: num1 = "2", num2 = "3"
Output: "6"

Example 2:

Input: num1 = "123", num2 = "456"
Output: "56088"

 

Constraints:

• 1 <= num1.length, num2.length <= 200
• num1 and num2 consist of digits only.
• Both num1 and num2 do not contain any leading zero, except the number 0 itself.

Solution : 

Just observe the solution and you will understand it normally. Few hints are : 

• The maximum length of the answer can be the sum of the length of two strings.
• Just multiply like you multiply the normally  as  a children of class 2nd.

class Solution { public:     string multiply(string num1, string num2) {         int a = num1.size();         int b = num2.size();               // create a string value that is include the result         string res(a+b, '0');         // multiply values with each other by running for loop         // substracting '0' from string char number makes it integer         for(int i=a-1; i>=0; i--) {             for(int j=b-1; j>=0; j--) {                 int di = (num1[i] - '0') * (num2[j] - '0') + (res[i+j+1]-'0');                 res[i+j+1] = di % 10 + '0';                 res[i+j] += di/10;             }         }         // check if there is it start with zero         for(int i=0; i<res.size(); i++) {             if(res[i]!='0') return res.substr(i);         }         return "0";     } };