Longest Substring Without Repeating Characters

Given a string, find the length of the longest substring without repeating characters.

Example 1:

Input: "abcabcbb"
Output: 3 
Explanation: The answer is "abc", with the length of 3. 

Example 2:

Input: "bbbbb"
Output: 1
Explanation: The answer is "b", with the length of 1.

Example 3:

Input: "pwwkew"
Output: 3
Explanation: The answer is "wke", with the length of 3. 
             Note that the answer must be a substring, "pwke" is a subsequence and not a substring.

class Solution {
    public int lengthOfLongestSubstring(String s) {
        int best_so_far = 0;
        HashMap<Character, Integer> map = new HashMap<>();
        int start = 0;
        for (int i = 0; i < s.length(); i++) {
            if (map.containsKey(s.charAt(i))) {
                if (map.get(s.charAt(i)) >= start) {
                    start = map.get(s.charAt(i)) + 1; // Because the previous character ( which was same) will not be
                                                      // considered while counting the new
                                                      // length
                }
            }
            best_so_far = Math.max(best_so_far, i - start + 1);
            map.put(s.charAt(i), i);
        }
        return best_so_far;
    }
}