代码随想录算法训练营第13天 | 239. 滑动窗口最大值 347.前 K 个高频元素

239. Sliding Window Maximum

# 用有趣方式取代max（max函数效率很低，本质是for循环）
# 单调队列：队尾插，队头删
# 需要使用双端队列deque
from collections import deque
class Solution(object):
    def maxSlidingWindow(self, nums, k):
        window = deque()
        res = []
        for i in range(0, len(nums)):
            if window and i - k + 1 > window[0]: # window非空，且最大元素的位置已经小于窗口的左边界了，则去掉队头元素（过期了）
                window.popleft()
            while window and nums[i] >= nums[window[-1]]: # window非空，且当前元素大于队尾元素，则把队尾元素删掉
                window.pop()
            window.append(i) # 把当前元素加进来
            if i >= k - 1: # 当前窗口里至少有k个元素，为了处理前k个元素
                res.append(nums[window[0]])
        return res

347. Top K Frequent Elements

import heapq
class Solution(object):
    def topKFrequent(self, nums, k):
        dic = {}
        for i in nums:
            dic[i] = dic.get(i, 0) + 1
        pq = []
        heapq.heapify(pq)
        for key,val in dic.items():
            val = val
            heapq.heappush(pq, (val, key))
            if len(pq) > k:
                heapq.heappop(pq)
        res = []
        for i in range(0, k):
            temp = heapq.heappop(pq)
            res.append(temp[1])
        return res