751. IP to CIDR

340. Longest Substring with At Most K Distinct Characters (Hard)

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.

Companies:
Facebook, Amazon, Google

Related Topics:
Hash Table, String, Sliding Window

Similar Questions:

• Longest Substring Without Repeating Characters (Medium)
• Longest Substring with At Most Two Distinct Characters (Hard)
• Longest Repeating Character Replacement (Medium)
• Subarrays with K Different Integers (Hard)
• Max Consecutive Ones III (Medium)

Solution 1.

// OJ: https://leetcode.com/problems/longest-substring-with-at-most-k-distinct-characters/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(1)
class Solution {
public:
    int lengthOfLongestSubstringKDistinct(string s, int k) {
        vector<int> m(128, 0);
        int i = 0, j = 0, ans = 0, cnt = 0;
        while (j < s.size()) {
            if (m[s[j++]]++ == 0) cnt++;
            while (cnt > k) {
                if (m[s[i++]]-- == 1) cnt--;
            }
            ans = max(ans, j - i);
        }
        return ans;
    }
};