The Multiply Strings problem asks you to multiply two non-negative integers represented as strings and return their product as a string — without converting to integer type. This Multiply Strings coding problem tests string-based arithmetic and the grade-school multiplication algorithm implemented at the character level.
Apple, Uber, Microsoft, Meta, Amazon, Google, Bloomberg, and Adobe ask this because it tests fundamental understanding of positional number systems and how to implement arithmetic from first principles. It's directly relevant to big integer libraries and arbitrary-precision arithmetic. The math, string, and simulation interview pattern is the core.
Grade-school multiplication with position mapping. For num1 of length m and num2 of length n, the product has at most m+n digits. Create an array result[m+n]. For each digit i from num1 and digit j from num2, their product contributes to positions i+j and i+j+1. Accumulate all contributions, carry forward, then convert to string (stripping leading zeros).
num1 = "23", num2 = "45".
String arithmetic problems require knowing the positional digit multiplication rule: digit i of num1 (from right) × digit j of num2 (from right) contributes to positions (len1-1-i) + (len2-1-j) in the result. Alternatively, iterate from right to left and accumulate into a result array. The carry propagation step is the same as in addition. Practice Add Binary, Add Strings, and Multiply Strings as a progression — each builds on positional arithmetic intuition.
