‹ DS&A interview · Socratic
DSA · Strings · #100

Longest Common Prefix

Module 62 · difficulty 2/5·⏱ 30:00starts on first keystroke

Write a function `longestCommonPrefix(strs)` that takes an array of strings `strs` and returns the longest string that is a prefix of every string in the array. If there is no common prefix, return the empty string `""`.

Examples
  • strs = ["flower", "flow", "flight"] → "fl" — All three share the prefix "fl".
  • strs = ["dog", "racecar", "car"] → "" — No common prefix exists.
  • strs = ["interspecies", "interstellar", "interstate"] → "inters"
Constraints
  • · 1 <= strs.length <= 200
  • · 0 <= strs[i].length <= 200
  • · strs[i] consists of only lowercase English letters.
Session phases
A · Clarify
B · Approach
C · Complexity
D · Edges
E · Code
F · Tradeoff
G · Score
Phase A — Clarify
Ask questions about input bounds, types, and edge constraints.
Ask the coach clarifying questions about the problem.
When you've covered this phase, advance to the next.