sliding window(滑动窗口)算法

class Solution(object):    def totalFruit(self, tree):        """        :type tree: List[int]        :rtype: int        """        count=collections.Counter()        left=ans=0        for i,val in enumerate(tree):            count[val]+=1            while (len(count)>=3):                count[tree[left]]-=1                if count[tree[left]]==0:                    del count[tree[left]]                left+=1            ans=max(ans,i-left+1)        return ans