题解 | #至多包含K种字符的子串#

import java.util.*;


public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param s string字符串 
     * @param k int整型 
     * @return int整型
     */
    public int longestSubstring (String s, int k) {
        // write code here
        int l = 0;
        int r = 0;
        int res = 0;
        HashSet<Character> hashSet = new HashSet<>();
        while (l < s.length()) {
            r = l;
            hashSet.clear();
            while (hashSet.size() <= k && r < s.length()) {
                hashSet.add(s.charAt(r));
                r++;
            }
            if (r == s.length()) {
                if (hashSet.size() <= k) {
                    res = Math.max(res, r - l);
                }
                if (hashSet.size() - 1 == k) {
                    res = Math.max(res, r - l - 1);
                }
                break;
            }
            res = Math.max(res, r - l - 1);
            l++;
        }
        return res;
    }
}