【Hot100】3. Longest substring without duplicate characters

Medium question
Given a string s , Please find out that there are no duplicate characters in it Longest substrings The length of .

Answer key ：
The sliding window
Define a map Data structure storage (k, v), among key The value is the character ,value Value is character position +1, Add 1 Indicates that the character is not repeated until after the character position .

Define the start position of non repeating substring as start, End position is end

With end Go back and forth , Will meet with [start, end] If the characters in the interval are the same , In this case, the character is used as key value , Get its value value , And update the start, here [start, end] There are no repeating characters in the interval

Whether updated or not start, Will update it map Data structure and results ans.

map Of value Save the subscript of the character directly for better understanding , stay map.get(c) And then +1 operation .

Code ：

class Solution {
    
    public int lengthOfLongestSubstring(String s) {
    
        int res = 0;
        Map<Character,Integer> map = new HashMap<>();
        for(int start = 0,end = 0;end < s.length(); end++){
    
            char c = s.charAt(end);
            if(map.containsKey(c)){
    
                // The equivalent character has not been saved for the second time , therefore map The subscript of the same character stored before is taken from ,start Update to next position of subscript 
                start = Math.max(map.get(c) + 1 ,start);
            }
            res = Math.max(end - start + 1,  res);

            map.put(c,end);

        }
        return res;

    }
}