最长不重复字符串 Java

import java.util.*;
import java.io.*;

public class Main {
	public static void main(String[] args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		StringTokenizer st = new StringTokenizer(br.readLine());
		char[] c = st.nextToken().toCharArray();
		Set<Character> set = new HashSet<>();
		int maxLength = 0;
		for (int l = 0, r = 0; r < c.length; r++) {
			while (set.contains(c[r])) { // 去除已有元素，左指针向右滑动
				set.remove(c[l]);
				l++;
			}
			set.add(c[r]); // 添加右指针上的元素
			if (set.size() > maxLength) maxLength = set.size();
		}
		System.out.println(maxLength);
	}
}

滑动窗口（双指针）~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~