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

给定一个字符串，找出最长的无重复子串。

	public static int lengthOfLongestSubstring(String s) {
		if (s == null || s.length() == 0)
			return 0;
		int maxlen = 1;
		boolean[] flag = new boolean[256];
		int start = 0;

		for (int i = 0; i < s.length(); i++) {
			char ch = s.charAt(i);
			if (flag[ch]) {
				maxlen = Math.max(maxlen, i - start);
				for (int j = start; j < i; j++) {
					if (s.charAt(j) == ch) {
						start = j + 1;
						break;
					}
					flag[s.charAt(j)] = false;
				}
			} else
				flag[ch] = true;
		}
		return Math.max(maxlen, s.length() - start);
	}