2021-01-27

215.数组中的第K个最大元素

class Solution:
    def findKthLargest(self, nums: List[int], k: int) -> int:
        if len(nums) == 1: return nums[0]
        mid = int(len(nums) // 2)
        left, right, mids = [], [], []
        for i in range(len(nums)):
            if nums[i] > nums[mid]:
                left.append(nums[i])
            elif nums[i] < nums[mid]:
                right.append(nums[i])
            else:
                mids.append(nums[i])
        if len(left) >= k:
            return  self.findKthLargest(left, k)
        elif len(mids) >= k - len(left):
            return nums[mid]
        else:
            return self.findKthLargest(right, k - len(left) - len(mids))

217.存在重复元素

class Solution:
    def containsDuplicate(self, nums: List[int]) -> bool:
        return len(set(nums)) < len(nums)

230.二叉搜索树中第K小的元素

class Solution:
    def kthSmallest(self, root, k):
        """
        :type root: TreeNode
        :type k: int
        :rtype: int
        """
        def gen(r):
            if r is not None:
                yield from gen(r.left)
                yield r.val
                yield from gen(r.right)
        
        it = gen(root)
        for _ in range(k):
            ans = next(it)
        return ans