[LeetCode160]Longest Substring with At Most Two Distinct Characters

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

For example, Given s = “eceba”,

T is "ece" which its length is 3.

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记得看到一个blog说：这种题，一般都在于用一个hash table 和两个reference。 不同之处在于如何update start point.

class Solution {
public:
    int lengthOfLongestSubstringTwoDistinct(string s) {
        if(s.empty()) return 0;
        int dict[256] = {0};
        int cnt = 0, start = 0, maxLen = 1;
        for (int i = 0; i<s.size(); ++i) {
            ++dict[s[i]];
            if (dict[s[i]] == 1) { // new char
                ++cnt;
                while (cnt > 2) {
                    --dict[s[start]];
                    if(!dict[s[start]]) --cnt; // mp[s[i] indicates: from start to current position, how many s[i] the substr has. if(!mp[s[start]]) then s[start] no longer exist we can --cnt;
                    ++start;
                }
            }
            maxLen = max(maxLen, i-start + 1);
        }
        return maxLen;
    }
};