Longest Substring Without Repeating Characters

Source

• lintcode: Longest Substring Without Repeating Characters

Given a string, find the length of the longest substring 
repeating characters.

Example
For example, the longest substring without repeating letters for
"abcabcbb" is "abc", which the length is 3.

For "bbbbb" the longest substring is "b", with the length of 1.

Challenge
O(n) time

Java

public class Solution {
    /**
     * @param s: a string
     * @return: an integer 
     */
    public int lengthOfLongestSubstring(String s) {
        if (s.length()==0) return 0;
        HashMap<Character, Integer> map = new HashMap<Character, Integer>();
        int max=0;

        for (int end=0, start=0; end<s.length(); ++end){
            if (map.containsKey(s.charAt(end))){
                start = Math.max(start, map.get(s.charAt(end))+1);
            }
            map.put(s.charAt(end), end);
            max = Math.max(max, end-start+1);
        }
        return max;   
    }
}