Compare Version Numbers - Video Solutions

Problem Overview: You are given two version strings such as "1.01" and "1.001". Each version is composed of revisions separated by dots. The task is to compare them numerically revision by revision and return whether one version is greater, smaller, or equal.

Approach 1: Split and Compare Each Component (O(n) time, O(n) space)

The most direct solution splits both version strings using the dot delimiter and compares the resulting revision numbers. Each component is parsed as an integer to ignore leading zeros. Iterate through both arrays simultaneously and compare corresponding revisions. If one version has fewer parts, treat missing revisions as 0. This approach is straightforward and easy to implement using built-in string utilities, making it a practical choice during interviews when clarity matters more than micro-optimizations.

Most languages provide efficient split operations, so implementation becomes a simple loop comparing integers. However, splitting creates extra arrays, which introduces O(n) space complexity. For extremely long version strings or memory-constrained environments, avoiding additional allocations can be beneficial. The approach relies purely on string manipulation and sequential iteration.

Approach 2: Two-pointer Comparison Traversal (O(n) time, O(1) space)

This method avoids splitting entirely by scanning both version strings using two pointers. Each pointer traverses its string and constructs the current revision number digit by digit until reaching a dot or the end. After parsing the current revision for both strings, compare the two integers. If they differ, return the result immediately. Otherwise, move past the dot and continue processing the next revision.

The key insight is that each revision can be built incrementally while traversing the string, eliminating the need for intermediate arrays. Missing revisions naturally evaluate to 0 once a pointer reaches the end of its string. This keeps space usage constant while still processing every character once, resulting in O(n) time complexity. This pattern frequently appears in problems involving segmented string comparisons.

Recommended for interviews: Start with the split-based approach because it clearly communicates the logic of comparing revision numbers. After that, mention the two-pointer traversal as an optimization that removes extra memory usage. Interviewers often expect candidates to recognize the two pointers technique for parsing structured string input efficiently.