题目：​​原题链接​​（中等）

标签：数组、双指针、滑动窗口

解法一：

class Solution:
    def totalFruit(self, tree: List[int]) -> int:
        ans = 0

        l, r = 0, 0
        window = collections.Counter()
        while r < len(tree):
            window[tree[r]] += 1
            while len(window) > 2:
                window[tree[l]] -= 1
                if window[tree[l]] == 0:
                    window.pop(tree[l])
                l += 1
            ans = max(ans, r - l + 1)
            r += 1

        return ans