Implement version string comparator with extensions

Q: Implement version string comparator with extensions

This question evaluates string parsing and comparison algorithms, handling of numeric versus lexical ordering and versioning semantics (including pre-release identifiers and ignored build metadata), within the Coding & Algorithms domain.

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This is a Medium difficulty Coding & Algorithms question, commonly asked during Technical Screen rounds at Nextdoor.

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Question

Implement a function compareVersions(a, b) that compares two software version strings. Each version consists of dot-separated numeric components (e.g., 1.02.
3). Treat missing trailing components as 0 and compare numerically, ignoring leading zeros. Extend the comparator to support optional pre-release identifiers (e.g., -alpha, -rc.
1) that sort before the corresponding release; compare pre-release identifiers by dot-separated tokens where numeric tokens are compared numerically and non-numeric tokens lexicographically; ignore build metadata (everything after '+'). Return -1 if a < b, 0 if equal, and 1 if a > b. Analyze time and space complexity and describe test cases covering tricky inputs (very long components, many segments, leading zeros, empty segments, pre-release ordering).

PracHub · Accepted Answer

def solution(a, b): def normalize(comp): if comp == '': return '0' i = 0 while i < len(comp) and comp[i] == '0': i += 1 return comp[i:] if i < len(comp) else '0' def cmp_num(x, y): x = normalize(x) y = normalize(y) if len(x) < len(y): return -1 if len(x) > len(y): return 1 if x < y: return -1 if x > y: return 1 return 0 parts_a = a.split('.') if a != '' else [''] parts_b = b.split('.') if b != '' else [''] for i in range(max(len(parts_a), len(parts_b))): comp_a = parts_a[i] if i < len(parts_a) else '0' comp_b = parts_b[i] if i < len(parts_b) else '0' result = cmp_num(comp_a, comp_b) if result != 0: return result return 0 def solution(a, b): def normalize_num(s): if s == '': return '0' i = 0 while i < len(s) and s[i] == '0': i += 1 return s[i:] if i < len(s) else '0' def cmp_num(x, y): x = normalize_num(x) y = normalize_num(y) if len(x) < len(y): return -1 if len(x) > len(y): return 1 if x < y: return -1 if x > y: return 1 return 0 def parse(version): main = version.split('+', 1)[0] if '-' in main: core, pre = main.split('-', 1) pre_parts = pre.split('.') if pre != '' else [''] else: core = main pre_parts = None core_parts = core.split('.') if core != '' else [''] return core_parts, pre_parts def cmp_core(parts_a, parts_b): for i in range(max(len(parts_a), len(parts_b))): comp_a = parts_a[i] if i < len(parts_a) else '0' comp_b = parts_b[i] if i < len(parts_b) else '0' result = cmp_num(comp_a, comp_b) if result != 0: return result return 0 def cmp_pre(pre_a, pre_b): if pre_a is None and pre_b is None: return 0 if pre_a is None: return 1 if pre_b is None: return -1 limit = min(len(pre_a), len(pre_b)) for i in range(limit): ta = pre_a[i] tb = pre_b[i] is_num_a = ta.isdigit() is_num_b = tb.isdigit() if is_num_a and is_num_b: result = cmp_num(ta, tb) if result != 0: return result elif is_num_a and not is_num_b: return -1 elif not is_num_a and is_num_b: return 1 else: if ta < tb: return -1 if ta > tb: return 1 if len(pre_a) < len(pre_b): return -1 if len(pre_a) > len(pre_b): return 1 return 0 core_a, pre_a = parse(a) core_b, pre_b = parse(b) result = cmp_core(core_a, core_b) if result != 0: return result return cmp_pre(pre_a, pre_b)

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Part 2: Compare Version Strings with Pre-Release Identifiers and Build Metadata

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