Remove Duplicate Characters from a String

📌 Definition:

📖 Detailed Explanation:

Iterate once, appending a character only if it has not been seen, tracking membership in an ordered set. O(n). Using an unordered set or sorting loses the original order.

💻 Solutions:

• Java
• JavaScript
• Python

public static String removeDuplicates(String s) {
    Set<Character> seen = new LinkedHashSet<>();
    for (char c : s.toCharArray()) seen.add(c);
    StringBuilder sb = new StringBuilder();
    for (char c : seen) sb.append(c);
    return sb.toString();
}

function removeDuplicates(s) {
  return [...new Set(s)].join('');
}

def remove_duplicates(s):
    return ''.join(dict.fromkeys(s))

🔑 Key Points:

• Track seen chars in a set
• Ordered set preserves first-seen order
• Append only unseen characters
• O(n) time, O(k) space

🌍 Real-World Example: