Leetcode-3 longest substring without duplicate characters

subject

Example 1:

 Input : s = "abcabcbb"
 Output : 3 
 explain :  Because the longest substring without repeating characters is  "abc", So its  The length is  3.

At first, I used violence myself , I found that some use cases tested, but , The time complexity is still relatively high

I learned a new way to solve this problem —— Slide window idea    

hypothesis s=“pwwkew”

Use the left and right pointers , Move the right pointer right to join the window , Move the left pointer right out of the window .

First judge hashset Whether it contains an element , If not, join set in , The right pointer continues to move right , Repeat the process ;

Code ：  The time complexity is O（n） n by s The length of

class Solution {
    public int lengthOfLongestSubstring(String s) {
        HashSet<Character> hash=new HashSet<>();
    	int len=s.length();
    	int count=0,left=-1;  // On the left side of the window 
    	for(int i=0;i<len;i++) {
    		if(i!=0)
    			hash.remove(s.charAt(i-1));  Gradually delete the data in the window 
    		while(left+1<len&&!hash.contains(s.charAt(left+1))) { // If the number is not in the window 
    			hash.add(s.charAt(left+1)); // Just join the window 
    			left++;
    		}
    		count=Math.max(count, left-i+1); // Update window length 
    	}
    	return count;
    }
}