无重复字符的最长子串

import java.util.HashMap;
import java.util.Map;
public class Main{
    public static void main(String[] args) {
        var a = lengthOfLongestSubstring("abacad");
        System.out.println(a);
    }
    static int lengthOfLongestSubstring(String s){
        int len = s.length();
        //ans记录结果
        int ans = 0;
        //map记录字母的步长
        Map<Character,Integer> map = new HashMap<>();
        for (int start = 0,end=0; end<len; end++) {
            char alpha = s.charAt(end);
            if(map.containsKey(alpha)){
                //如果map记录了alpha字符，就更新start
                  start = Math.max(map.get(alpha),start);
            }
            //将字符的步长记录
            map.put(alpha, end+1);
            //更新最长的字符串步长
            ans = Math.max(ans,end-start+1);
        }
        return ans;
    }
}