159. Longest Substring with At Most Two Distinct Characters

159. Longest Substring with At Most Two Distinct Characters (Hard)

Given a string s , find the length of the longest substring t  that contains at most 2 distinct characters.

Example 1:

Input: "eceba"
Output: 3
Explanation: t is "ece" which its length is 3.

Example 2:

Input: "ccaabbb"
Output: 5
Explanation: t is "aabbb" which its length is 5.

Companies:
Google, Amazon

Related Topics:
Hash Table, Two Pointers, String, Sliding Window

Similar Questions:

• Longest Substring Without Repeating Characters (Medium)
• Sliding Window Maximum (Hard)
• Longest Substring with At Most K Distinct Characters (Hard)
• Subarrays with K Different Integers (Hard)

Solution 1.

// OJ: https://leetcode.com/problems/longest-substring-with-at-most-two-distinct-characters/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(1) 
class Solution {
public:
    int lengthOfLongestSubstringTwoDistinct(string s) {
        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 > 2) {
                if (m[s[i++]]-- == 1) --cnt;
            }
            ans = max(ans, j - i);
        }
        return ans;
    }
};