3. Longest Substring Without Repeating Characters

s[j,i]表示以字母i结尾的最长的无字母重复的substring；

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

注意：
j的更新不能直接：j = charPosition.get(s.charAt(i)) + 1;
例如测试用例“abba”，当i=3时，j将被从2更新为1.