LeetCode 340. Longest Substring with At Most K Distinct Characters 雙指針

Given a string, find the length of the longest substring T that contains at most k distinct characters.

Example 1:

Input: s = "eceba", k = 2
Output: 3
Explanation: T is "ece" which its length is 3.

Example 2:

Input: s = "aa", k = 1
Output: 2
Explanation: T is "aa" which its length is 2.

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沒想明白自己爲啥沒有一次AC

class Solution:
    def lengthOfLongestSubstringKDistinct(self, s: str, k: int) -> int:
        if (k == 0):
            return 0
        l = len(s)
        x,y,curk,res = 0,0,0,0
        dic = {}
        for y in range(l):
            if (s[y] in dic):
                dic[s[y]] += 1
            else:
                curk += 1
                dic[s[y]] = 1
                while (curk > k):
                    dic[s[x]] -= 1
                    if (dic[s[x]] == 0):
                        curk -= 1
                        dic.pop(s[x]) #bug1: miss this line
                    x += 1
            res = max(res,y-x+1)
        return res