leetcode-java-3. Longest Substring Without Repeating Characters

思路：
用HashMap动态存储字符串的每个不重复的子字符串；
当有重复字符出现时，动态更新子字符串的最大值和更新HashMap

public class Solution {    public int lengthOfLongestSubstring(String s) {        HashMap<Character,Integer> map = new HashMap<Character,Integer>();        int removeStart = 0,            max = 0,            i = 0;        for(;i < s.length();i++) {            char ch = s.charAt(i);            if(!map.containsKey(ch)) {                map.put(ch,i);            } else{                max = Math.max(max,map.size());                while(map.containsKey(ch)) {                    map.remove(s.charAt(removeStart));                    removeStart++;                }                map.put(ch,i);            }        }        // 当字符串无重复时，max还是0，则需要更新        max = Math.max(max, map.size());        return max;    }}