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.

思路：引入Map记录已经存在的字符，记录好最长字符的开始、结束位置。o(2n)

public int lengthOfLongestSubstring(String s) {
		if (null == s || s.length() == 0)
			return 0;
		int max = 1;
		Map<Character, Integer> map = new HashMap<Character, Integer>();
		int start = 0, end = 0, hit = 0;
		while (end < s.length()) {
			char next = s.charAt(end);
			if (!map.containsKey(next)) {
				map.put(next, end);
				end++;
				max = max < (end - start) ? (end - start) : max;
			} else {
				hit = map.get(next);
				
				while(start<= hit){
					map.remove(s.charAt(start));
					start++;
				}
				map.put(next, end);
				end++;
			}
		}
		return max;
	}

牛人的解法，不用清除map中的数据，o(n)

  public int lengthOfLongestSubstring(String s) {
        if (s.length()==0) return 0;
        HashMap<Character, Integer> map = new HashMap<Character, Integer>();
        int max=0;
        for (int i=0, j=0; i<s.length(); ++i){
            if (map.containsKey(s.charAt(i))){
                j = Math.max(j,map.get(s.charAt(i))+1);
            }
            map.put(s.charAt(i),i);
            max = Math.max(max,i-j+1);
        }
        return max;
    }