代码1

j在i之前，遇到一个重复的就一直增加j，直到j等于i
Runtime: 4 ms, faster than 89.11% of Java online submissions for Longest Substring Without Repeating Characters.

class Solution {
    public int lengthOfLongestSubstring(String s) {
        int[] arr = new int[256];
        int length = 0;
        for (int i = 0, j = 0; i < s.length(); i++) {
            arr[s.charAt(i)]++;
            while (arr[s.charAt(i)] > 1) {
                arr[s.charAt(j++)]--;
            }
            length = Math.max(length, i - j + 1);
        }
        return length;
    }
}