hot100_3.java

import java.util.*;
/**无重复字符的最长子串
 * 输入：abcabcbb 输出：3
 */
public class hot100_3 {

    public static int lengthOfLongestSubstring(String s) {

        // 存储字符最后出现的位置
        HashMap<Character, Integer> map = new HashMap<>();

        int left = 0;
        int maxLen = 0;

        for (int right = 0; right < s.length(); right++) {

            char c = s.charAt(right);

            // 如果字符重复
            // 并且重复字符在窗口内部
            if (map.containsKey(c) && map.get(c) >= left) {
                left = map.get(c) + 1;
            }

            // 更新字符位置
            map.put(c, right);

            // 更新最大长度
            maxLen = Math.max(maxLen, right - left + 1);
        }

        return maxLen;
    }

    public static void main(String[] args) {

        Scanner sc = new Scanner(System.in);

        String s = sc.nextLine();

        System.out.println(lengthOfLongestSubstring(s));
    }
}