HashMap Problems in Java

This repository contains HashMap-based problems implemented in Java.
Each problem focuses on solving real-world challenges using hashing, frequency counting, and mapping.

---

📌 Problems

🔹 1. Frequency Counter

• Problem: Read a string and count the frequency of each character.
• Approach:
  • Use a HashMap<Character, Integer>.
  • Traverse the string and update frequency.
  • Example:

    Input: "programming"
    Output: {p=1, r=2, o=1, g=2, a=1, m=2, i=1, n=1}
    

---

🔹 2. Anagram Grouping

• Problem: Given an array of strings, group all anagrams together.
• Approach:
  • Sort each word’s characters → use sorted string as the key.
  • Store original word in a list mapped to that key.
  • Example:

    Input: ["eat","tea","tan","ate","nat","bat"]
    Output: [["eat","tea","ate"], ["tan","nat"], ["bat"]]
    

---

🔹 3. First Non-Repeated Character

• Problem: Find the first non-repeated character in a string.
• Approach:
  • Use a LinkedHashMap to preserve insertion order.
  • Count occurrences.
  • Return first character with frequency = 1.
  • Example:

    Input: "swiss"
    Output: 'w'
    

---

🔹 4. Sorting by Values

• Problem: Sort a HashMap by its values.
• Approach:
  • Convert entrySet() into a list.
  • Sort using a custom comparator based on values.
  • Insert back into LinkedHashMap to maintain order.
  • Example:

    Input: {a=5, b=2, c=8, d=3}
    Output: {b=2, d=3, a=5, c=8}
    

---

🔹 5. Duplicate Elements in Array

• Problem: Find duplicate elements and their counts in an array.
• Approach:
  • Use a HashMap<Integer, Integer> to store frequencies.
  • Print numbers with count > 1.
  • Example:

    Input: [4, 5, 6, 4, 7, 5, 6, 6]
    Output: {4=2, 5=2, 6=3}