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2108 - Find First Palindromic String in the Array (Easy)

https://leetcode.com/problems/find-first-palindromic-string-in-the-array/

Problem Statement​

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.

Approach 1: Check each word​

There are several ways to check if a string is a palindrome or not.

Long and Efficient ​

bool isPalindrome(const string& s) {
    for (int i = 0; i < s.size() / 2; i++) {
        if (s[i] != s[s.size() - i - 1])
            return false;
    }
    return true;
}

Shorter but not efficient ​

bool isPalindrome(const string& s) {
    string t = s;
    reverse(t.begin(), t.end());
    return s == t;
}

Shortest but not efficient ​

bool isPalindrome(const string& s) {
    return s == string(s.rbegin(), s.rend());
}

Shortest but efficient ​

bool isPalindrome(const string &s) {
    return equal(s.begin(), s.begin() + s.size() / 2, s.rbegin());
}

We just need to iterate each string and check if the target sss is a palindrome, return the string if so.

Written by @wingkwong
class Solution {
public:
    bool isPalindrome(const string& s) {
        return equal(s.begin(), s.begin() + s.size() / 2, s.rbegin());
    }
    
    string firstPalindrome(vector<string>& words) {
        for (auto s : words) {
            if (isPalindrome(s)) {
                return s;
            }
        }
        return "";
    }
};