[LeetCode] Longest Substring Without Repeating Characters

Thought:
    Try to implement a O(n) method using just one scan of the String.
    Use a HashMap to track which letter has occured.

Code:

public class Solution {
    public int lengthOfLongestSubstring(String s) {
        int max = 0;
        int length = 0;
        HashMap<Character, Integer> index = new HashMap<Character, Integer>();
        for( int i = 0; i < s.length(); i++ ){
            char temp = s.charAt(i);
            if( !index.containsKey(temp) ){
                index.put(temp,i);
                length++;
                max = Math.max(length, max);
            }else{
                i = index.get(temp);
                index.clear();
                length = 0;
            }
        }
        return max;
    }
}