def double_pointer(nums: List[int], target: int):
    n = len(nums)
    buf = {}
    l = 0
    res = []

    for r, x in enumerate(nums):
        while x in buf:
            buf.pop(nums[l])
            l += 1
        buf[x] = r
        if x == target:
            res.append(l)
    return res

def sliding_window(nums: List[int], k: int):
    # 这里的输入k也可以是别的什么条件，反正滑动窗口的题目，就是要保证窗口内的元素满足某种条件
    n = len(nums)
    i = 0 # 窗口左边界
    s = 0 # 窗口内元素的某个条件
    res = inf # 结果是最长超过k的子数组的长度
    # 窗口右边界 x = nums[j]
    for j, x in enumerate(nums):
        s += x # 更新窗口内元素
        while <窗口内元素符合条件>:
            res =  # 更新结果
            s -= nums[i] # 窗口左边界右移，直到窗口内元素不满足条件
            i += 1
    return res if res != inf else -1

d = {} # d = dict()
for c in s:
    d[c] = d.get(c, 0) + 1

buf = defaultdict(int)
buf = Counter(s)