0043. Multiply Strings

https://leetcode.com/problems/multiply-strings

Description

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.

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