How can I find the first palindromic string in an array?

You can find the first palindromic string by using a two-pointer technique to check if each word in the array is palindromic. Return the first palindrome you encounter.

What is the time complexity of this problem?

The time complexity is O(N * M), where N is the number of words and M is the length of the longest word.

What does it mean for a string to be palindromic?

A palindromic string is one that reads the same forward and backward, such as 'madam' or 'ada'.

Can this problem be solved with a brute force approach?

Yes, but using a two-pointer approach ensures a more efficient solution by checking each word only once and stopping early if a palindrome is found.

What pattern is applied in this problem?

This problem uses a two-pointer scanning technique, which is effective for checking palindromic strings in a systematic manner.

#2108

Easy

auto_awesome双·指针·invariant

LeetCode 题解工作台

找出数组中的第一个回文字符串

给你一个字符串数组 words ，找出并返回数组中的第一个回文字符串。如果不存在满足要求的字符串，返回一个空字符串 "" 。回文字符串的定义为：如果一个字符串正着读和反着读一样，那么该字符串就是一个回文字符串。示例 1：输入： words = ["abc","car","ada",…

数组双指针字符串

题目描述

给你一个字符串数组 words ，找出并返回数组中的 第一个回文字符串 。如果不存在满足要求的字符串，返回一个 空字符串 "" 。

回文字符串 的定义为：如果一个字符串正着读和反着读一样，那么该字符串就是一个 回文字符串 。

示例 1：

输入：words = ["abc","car","ada","racecar","cool"]
输出："ada"
解释：第一个回文字符串是 "ada" 。
注意，"racecar" 也是回文字符串，但它不是第一个。

示例 2：

输入：words = ["notapalindrome","racecar"]
输出："racecar"
解释：第一个也是唯一一个回文字符串是 "racecar" 。

示例 3：

输入：words = ["def","ghi"]
输出：""
解释：不存在回文字符串，所以返回一个空字符串。

提示：

1 <= words.length <= 100
1 <= words[i].length <= 100
words[i] 仅由小写英文字母组成

lightbulb

解题思路

方法一：模拟

我们遍历数组 words，对于每个字符串 w，判断其是否为回文字符串，如果是，则返回 w，否则继续遍历。

判断一个字符串是否为回文字符串，可以使用双指针，分别指向字符串的首尾，向中间移动，判断对应的字符是否相等。如果遍历完整个字符串，都没有发现不相等的字符，则该字符串为回文字符串。

时间复杂度 $O(L)$ ，其中 $L$ 为数组 words 中所有字符串的长度之和。空间复杂度 $O(1)$ 。

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class Solution:
    def firstPalindrome(self, words: List[str]) -> str:
        return next((w for w in words if w == w[::-1]), "")

speed

复杂度分析

指标	值
时间	O(N \cdot M)
空间	O(1)

psychology

面试官常问的追问

外企场景

question_mark
Look for efficient handling of string iteration.
question_mark
Ensure the candidate applies the two-pointer technique correctly.
question_mark
Check if the solution returns early upon finding the first palindromic word.

warning

常见陷阱

外企场景

error
Failing to iterate through the array properly.
error
Not returning early when the first palindromic word is found.
error
Incorrectly assuming that checking palindromic status is trivial without using a systematic approach like two-pointer scanning.

swap_horiz

进阶变体

外企场景

arrow_right_alt
Return the first palindrome with specific character conditions (e.g., only vowels).
arrow_right_alt
Handle larger inputs efficiently with O(N * M) time complexity.
arrow_right_alt
Extend to find the longest palindromic string in the array.

help

常见问题

外企场景

继续练习

#2109 向字符串添加空格 #1961 检查字符串是否为数组前缀 #1898 可移除字符的最大数目