LeetCode之Longest Substring Without Repeating Characters

原题描述

3.Longest Substring Without Repeating Characters

Given a string, find the length of the longest substring without repeating characters.
Examples:
Given "abcabcbb", the answer is "abc", which the length is 3.
Given "bbbbb", the answer is "b", with the length of 1.
Given "pwwkew", the answer is "wke", with the length of 3. Note that the answer must be a substring, "pwke" is a subsequence and not a substring.

解题思路

遍历字符串，用一个容器存放已读的字符，用来判断是否存在重复字符，用一个max记录当前下最大的不重复子串长度。对于"abcb"这种，到了第二个b的时候，可以发现两个b之间是不可能有不重复子串的，所以新的子串要从c处开始记录即b.index+1处，用start记录子串的新起点，为了防止出现“abcba”这种b的重复先出现了后，将新start设为2了,下次a出来以后start再给设为1，要在原start和新start之间取最大值。容器选用map<Character, Integer>对应子串中每个字符的index。这样遍历一遍后得的max即为结果

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