LeetCode #340. Longest Substring with At Most K Distinct Characters

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本文介绍了一种算法，用于寻找字符串中包含最多k种不同字符的最长子串。通过使用滑动窗口和哈希表，该算法能有效地解决这一问题。示例包括输入字符串eceba和k=2时，输出为ece，长度为3；输入aa和k=1时，输出为aa，长度为2。

题目描述：

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.

class Solution {
public:
    int lengthOfLongestSubstringKDistinct(string s, int k) {
        if(k<=0) return 0;
        unordered_map<int,int> count;
        int i=0, j=0;
        int max_length=INT_MIN;
        while(j<s.size())
        {
            if(count.size()<=k)
            {
                max_length=max(max_length,j-i);
                count[s[j]]++;
                j++;
            }
            while(count.size()>k)
            {
                count[s[i]]--;
                if(count[s[i]]==0) count.erase(s[i]);
                i++;
            }
        }
        if(count.size()<=k) max_length=max(max_length,j-i);
        return max_length;
    }
};