3. Longest Substring Without Repeating Characters

Posted 2021-01-01 gopanama

自己方法复杂度比较高

可以O(n)的方法，遍历一遍 用两个指针记录maxstring的位置 然后遇到跟hashmap里重复的就更新指针
https://leetcode.com/problems/longest-substring-without-repeating-characters/discuss/1729/11-line-simple-Java-solution-O(n)-with-explanation

 

 

 

 1 //Old
 2 class Solution {
 3     public int lengthOfLongestSubstring(String s) {
 4         char[] arr = s.toCharArray();
 5         int max = 0;
 6         for(int i = 0; i < arr.length; i++) {
 7             max = Math.max(max, dfs(arr, new ArrayList<>(), i));
 8         }
 9         return max;
10         
11     }
12     
13     public int dfs(char[] arr, List<Integer> list, int i) {
14         if(i >= arr.length || list.contains((int)arr[i])) return 0;
15         list.add((int)arr[i]);
16         return dfs(arr, list, i+1)+1;    
17     }
18     
19 }
20 
21 
22 
23 
24 //New
25    public int lengthOfLongestSubstring(String s) {
26         if (s.length()==0) return 0;
27         HashMap<Character, Integer> map = new HashMap<Character, Integer>();
28         int max=0;
29         for (int i=0, j=0; i<s.length(); ++i){
30             if (map.containsKey(s.charAt(i))){
31                 j = Math.max(j,map.get(s.charAt(i))+1);
32             }
33             map.put(s.charAt(i),i);
34             max = Math.max(max,i-j+1);
35         }
36         return max;
37     }