Longest substring without duplicate characters

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

• We define the starting 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.
• Time complexity ：O（n）

Code ：

 public int lengthOfLongestSubstring(String s) {

        int length=s.length();

        int max=0;

        // Store characters and 

        Map<Character,Integer> map =new HashMap<>();

        for (int start = 0,end=0; end <length ; end++) {

            char element=s.charAt(end);

            if (map.containsKey(element)){

                // To prevent continuous repetition of characters , Here is a judgment 

                //+1 Indicates that the next element after this element is the beginning of the non repeating string 

                start=Math.max(map.get(element)+1,start);

            }

            max=Math.max(max,end-start+1);

            // Save the last location of this node ;

            map.put(element,end);

        }

        return max;

    }