Leetcode #14: Longest Common Prefix
In this guide, we solve Leetcode #14 Longest Common Prefix in Python and focus on the core idea that makes the solution efficient.
You will see the intuition, the step-by-step method, and a clean Python implementation you can use in interviews.
Problem Statement
Write a function to find the longest common prefix string amongst an array of strings. If there is no common prefix, return an empty string "".
Quick Facts
- Difficulty: Easy
- Premium: No
- Tags: Trie, Array, String
Intuition
Prefix queries are most efficient with a trie.
Each character transitions to the next node in the tree.
Approach
Insert words into the trie and traverse by characters for queries.
Track terminal markers to distinguish full words from prefixes.
Steps:
- Build the trie.
- Traverse for each query.
- Return matches or validations.
Example
Input: strs = ["flower","flow","flight"]
Output: "fl"
Python Solution
class Solution:
def longestCommonPrefix(self, strs: List[str]) -> str:
for i in range(len(strs[0])):
for s in strs[1:]:
if len(s) <= i or s[i] != strs[0][i]:
return s[:i]
return strs[0]
Complexity
The time complexity is , where and are the length of the string array and the minimum length of the strings, respectively. The space complexity is .
Edge Cases and Pitfalls
Watch for boundary values, empty inputs, and duplicate values where applicable. If the problem involves ordering or constraints, confirm the invariant is preserved at every step.
Summary
This Python solution focuses on the essential structure of the problem and keeps the implementation interview-friendly while meeting the constraints.