🧑‍💻 LeetCode 2351 — Finding the First Letter to Appear Twice 🔥

In coding, handling strings efficiently is crucial, especially when working with algorithms to identify patterns. Today, we’ll explore LeetCode Problem 2351, “First Letter to Appear Twice.” This blog post dives into several approaches to solve this problem efficiently in Java, with detailed explanations for each solution.

🤔 Problem Statement

Level 🔥 Easy

Given a string s containing only lowercase letters, find the first character that appears at least twice. You are guaranteed that there’s at least one such character in s.

Example:

• Input: "abccbaacz"
• Output: 'c'
• Input: "abcdd"
• Output: 'd'

💡 Solution

✍ Approach 1: Using a HashSet to Track Seen Characters

The initial solution uses a HashSet to store each character as we encounter it. The goal is to check if a character has already been seen. If yes, that’s our answer since it’s the first one appearing twice. If not, we add it to our HashSet .

import java.util.HashSet;

public class Solution {
    public char repeatedCharacter(String s)…