Compare Version Numbers - Video Solutions

Problem Overview: You receive two version strings such as "1.02.3" and "1.2.003". Each dot-separated segment represents a revision number. Compare revisions from left to right and determine whether version1 is greater, smaller, or equal to version2 while ignoring leading zeros.

Approach 1: Split and Compare Each Component (Time: O(n), Space: O(n))

The direct solution splits both version strings using the dot delimiter and compares corresponding components one by one. Convert each segment to an integer so leading zeros like "001" and "1" become equivalent. Iterate through the longer of the two lists; if one version runs out of segments, treat the missing revision as 0. As soon as a pair of integers differs, return 1 or -1. If every segment matches, the versions are equal.

This approach is simple and readable. Most languages provide built-in string splitting and integer parsing, which keeps implementation short. The tradeoff is extra memory for storing arrays of revision components. Time complexity is O(n) where n is the total length of both version strings, and space complexity is also O(n) due to the split arrays. The method mainly relies on basic string processing.

Approach 2: Two-pointer Comparison Traversal (Time: O(n), Space: O(1))

This approach avoids splitting the strings entirely. Instead, traverse both version strings using two pointers. At each step, parse the next numeric segment by building the integer value until a dot or the end of the string appears. After extracting the numbers from both strings, compare them immediately. If one value is larger, return the result; otherwise continue scanning the next segment.

If one pointer reaches the end earlier, treat subsequent segments of the other version as integers and compare them against zero. This method processes characters directly and never allocates intermediate arrays. Time complexity remains O(n) since each character is visited once, but space complexity drops to O(1). The traversal pattern resembles classic two pointers techniques applied to sequential parsing.

Recommended for interviews: Start with the split-and-compare method to demonstrate the core idea clearly. Interviewers often accept it because the logic is straightforward and easy to verify. The two-pointer traversal is the stronger solution. It eliminates extra memory allocations and shows deeper control over string parsing and pointer movement. Candidates who implement the constant-space approach demonstrate stronger algorithmic thinking and familiarity with low-level string manipulation.