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NeetCode #187LC-2108EasyTwo Pointers
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#187 · #2108 · Find First Palindromic String in the Array(找出数组中的第一个回文字符串)

📌 Problem Statement & Constraints

Given an array of strings words, return the first palindromic string. If there is no such string, return an empty string. Constraints: 1 <= words.length <= 100, 1 <= words[i].length <= 100.

💡 Core Algorithmic Approaches

  1. Iterate the array in order and test each word for palindromicity.
  2. The first word that is a palindrome is the answer.
  3. A palindrome test is a two-pointer scan from the ends, or the slice comparison w == w[::-1].
  4. Return the empty string if none qualifies.

💻 Benchmark Python3 Implementation

class Solution:
    def firstPalindrome(self, words: List[str]) -> str:
        for w in words:
            if w == w[::-1]:           # slice comparison is O(len(w))
                return w
        return ""

⚡ Complexity Deep Dive

⏱️ Time Complexity
O(total characters in the worst case): each word is tested once with a linear palindrome check.
💾 Space Complexity
O(len(w)) for the reversed slice of the current word (O(1) extra if a two-pointer check is used instead).

⚠️ Interview Pitfalls & Follow-ups

  • Returning None: the contract requires an empty string.
  • Testing only the first and last characters: a full check is needed.
  • Sorting or scanning for the longest palindrome: the requirement is the first in input order.
  • Using a two-pointer check to save the slice allocation: a valid micro-optimisation, but the slice version is clearer and the constraints are tiny.