[LeetCode]Longest Substring with At Most Two Distinct Characters

和Longest Substring without Repeating Character是非常类似的题目，区别只是条件稍有不同，本质的做法都是一样的。可以用sliding window解，时间复杂度O(n)，空间复杂度O(n)，代码如下：

	class Solution {
	public:
	int lengthOfLongestSubstringTwoDistinct(string s) {
	int len = s.size(), left = 0, maxLen = 0;
	unordered_map<char, int> map;
	for(int i = 0; i < len; ++i)
	{
	++map[s[i]];
	while(map.size() > 2)
	{
	char c = s[left++];
	--map[c];
	if(!map[c])map.erase(c);
	}
	maxLen = max(maxLen, i - left + 1);
	}
	return maxLen;
	}
	};

view raw Longest Substring with At Most Two Distinct Characters.cpp hosted with ❤ by GitHub