[LeetCode] 2108. Find First Palindromic String in the Array

Given an array of strings words, return the first palindromic string in the array. If there is no such string, return an empty string "".

A string is palindromic if it reads the same forward and backward.

Example 1:
Input: words = ["abc","car","ada","racecar","cool"]
Output: "ada"
Explanation: The first string that is palindromic is "ada".
Note that "racecar" is also palindromic, but it is not the first.

Example 2:
Input: words = ["notapalindrome","racecar"]
Output: "racecar"
Explanation: The first and only string that is palindromic is "racecar".

Example 3:
Input: words = ["def","ghi"]
Output: ""
Explanation: There are no palindromic strings, so the empty string is returned.

Constraints:
1 <= words.length <= 100
1 <= words[i].length <= 100
words[i] consists only of lowercase English letters.

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 。

思路

找到 input 数组里第一个出现的回文串。

复杂度

时间O(mn) - m个单词，单词平均长度为n
空间O(1)

代码

Java实现

class Solution {
    public String firstPalindrome(String[] words) {
        for (String w : words) {
            if (helper(w)) {
                return w;
            }
        }
        return "";
    }
 
    public boolean helper(String word) {
        int left = 0;
        int right = word.length() - 1;
        while (left < right) {
            if (word.charAt(left) != word.charAt(right)) {
                return false;
            }
            left++;
            right--;
        }
        return true;
    }
}

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2108. Find First Palindromic String in the Array