Multiply Strings

Multiply Strings is a Medium Data Structures and Algorithms interview problem you can solve, run and submit on Thita.ai. It belongs to the String Manipulation Patterns pattern, in the Multiply Strings (Manual Simulation) subpattern.

Problem statement

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.

Topics and companies

Topics: Math, String, Simulation.

Reported in interviews at Facebook, Microsoft, Amazon, Square, Apple, Bloomberg, Two Sigma, ByteDance.

How to practise Multiply Strings on Thita.ai

Starter code is provided in C, C#, C++, Go, Java, JavaScript and Python. Your solution runs against 5 test cases for this problem, with the AI coach available for a hint when you are stuck rather than a finished answer. The reference solution runs in O(m * n) time and O(m + n) space.

Open Multiply Strings in the code editor, or read the Multiply Strings editorial for a worked solution with its approach and complexity analysis.

Where Multiply Strings sits in the DSA pattern sheet

• String Manipulation Patterns pattern guide
• Multiply Strings (Manual Simulation) subpattern
• The full DSA patterns sheet
• All coding practice problems

Problems related to Multiply Strings

Other problems that use the same Multiply Strings (Manual Simulation) and String Manipulation Patterns techniques:

• Add Binary — Easy, same subpattern
• Add to Array-Form of Integer — Easy, same subpattern
• Plus One — Easy, same subpattern
• Diagonal Traverse — Medium, same pattern
• Find All Duplicates in an Array — Medium, same pattern
• Find All Numbers Disappeared in an Array — Easy, same pattern