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longest-substring-with-at-most-two-distinct-characters

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Description

https://leetcode.com/problems/longest-substring-with-at-most-two-distinct-characters/

Solution

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class Solution {
public:
    int lengthOfLongestSubstringTwoDistinct(string s) {
        int maxLens = 0;
        int curLens = 0;
        unordered_map<char, int> counter;
        int preIndex = 0;
        for (int i = 0; i < s.size(); ++i) {
            counter[s[i]] += 1;
            while (counter.size() > 2) {
                counter[s[preIndex]] -= 1;
                if (counter[s[preIndex]] == 0) counter.erase(s[preIndex]);
                preIndex += 1;
                curLens -= 1;
            }
            curLens += 1;
            maxLens = max(maxLens, curLens);
        }
        return maxLens;
    }
};