查找一个字符串不重复最长的串

import java.util.HashMap;
import java.util.Map;

public class MyStringUtils {
    public static int getMaxLenght(String s) {
        int n = s.length();
        int ans = 0;//最大不连续长度
        int start = 0;//重复字符串位置
        int from = 0;//不重复开始的字符串开始
        int last = 0;//不重复开始的字符串结束
        Map<Character, Integer> map = new HashMap<>();
        for (int end = 0; end < n; end++) {
            char alpha = s.charAt(end);
            if (map.containsKey(alpha)) {
                start = Math.max(map.get(alpha), start);
            }
            if(end - start >ans){
                System.out.println(start);
                System.out.println(end);
                last = end;
                from = start;
            }
            ans = Math.max(ans, end - start );//最大不连续数

            map.put(alpha, end );
        }

        System.out.println(s.substring(from+1,last+1));
        return ans;
    }

    public static void main(String[] args) {
        int wangzfabedfpo = MyStringUtils.getMaxLenght("wangzfawbaedatpo");
        System.out.println(wangzfabedfpo);
    }

}