LongestUniqueSubstring.java

import java.util.HashMap;

class LongestUniqueSubstring {
    static final int MAX_CHAR = 26;

    static int bruteForce(String s) {
        int n = s.length();
        int res = 0;

        for (int i = 0; i < n; i++) {

            // Initializing all characters as not visited
            boolean[] vis = new boolean[MAX_CHAR];

            for (int j = i; j < n; j++) {

                // If current character is visited
                // Break the loop
                if (vis[s.charAt(j) - 'a'] == true)
                    break;

                    // Else update the result if this window is larger,
                    // and mark current character as visited.
                else {
                    res = Math.max(res, j - i + 1);
                    vis[s.charAt(j) - 'a'] = true;
                }
            }
        }
        return res;
    }

    static   int findLongestSubstringWithoutRepeating(String s) {
        HashMap<Character, Integer> charIndexMap = new HashMap<>();
        int maxLength = 0;
        int start = 0;

        for (int end = 0; end < s.length(); end++) {
            char currentChar = s.charAt(end);

            if (charIndexMap.containsKey(currentChar)) {
                start = Math.max(start, charIndexMap.get(currentChar) + 1);
            }

            charIndexMap.put(currentChar, end);
            maxLength = Math.max(maxLength, end - start + 1);
        }

        return maxLength;
    }

    public static void main(String[] args) {
        String s = "geeksforgeeks";
        System.out.println(bruteForce(s));
        System.out.println(findLongestSubstringWithoutRepeating(s));
    }
}