题目描述

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.

代码

    public static int lengthOfLongestSubstring(String s) {

        if (s == null) {
            return 0;
        }

        if (s.length() == 0 || s.length() == 1) {
            return s.length();
        }

        char[] c = s.toCharArray();

        // barrier：0~i中，第一个不重复字符的位置
        int barrier = 0;
        int maxLen = 1;

        for (int i = 1; i < c.length; i++) {
            for (int j = i - 1; j >= barrier; j--) {
                if (c[i] == c[j]) {
                    // 第一个不重复字符的位置为j+1，因为每次j从i-1递减到barrier
                    barrier = j + 1;
                    break;
                }
            }
            maxLen = Math.max(maxLen, i - barrier + 1);
        }

        return maxLen;
    }