3. [leetcode] Longest Substring Without Repeating Characters

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

Examples

Given "abcabcbb", the answer is "abc", which the length is 3.

Given "bbbbb", the answer is "b", with the length of 1.

Given "pwwkew", 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.

Solutions

HashMap + two pointers

public int lengthOfLongestSubstring(String s) {
        if(s == null || s.length() == 0){
            return 0;
        }
        Map<Character, Character> map = new HashMap();
        int j = 0;
        int max  = 0;
        char[] ch = s.toCharArray();
        for(int i = 0; i <ch.length; i++){
            while(j < ch.length && !map.containsKey(ch[j])){
                map.put(ch[j], ch[j]);
                j++;
                if(j - i > max){
                    max = j - i;
                }
            }
            map.remove(ch[i]);
        }
        return max;
}