[리트코드]3-8회차

https://leetcode.com/problems/minimum-absolute-difference-in-bst/?envType=study-plan-v2&envId=top-interview-150

 

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution(object):
    def dfs(self, root, parents, ans):
        if not root:
            return ans
        for parent in parents:
            temp = abs(parent - root.val)
            if temp < ans:
                ans = temp
            
        parents.append(root.val)
        if root.left:
            ans = self.dfs(root.left, parents, ans)
        if root.right:
            ans = self.dfs(root.right, parents, ans)
            
        return ans

    
    def getMinimumDifference(self, root):
        """
        :type root: Optional[TreeNode]
        :rtype: int
        """
        parents = []
        ans = (100000) + 1
        ans = self.dfs(root, parents, ans)
        
        return ans

풀긴풀었지만.. 뭐.. 역시 재귀방식이기도하고 너무 느리다.

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution(object):
    
    def getMinimumDifference(self, root):
        """
        :type root: Optional[TreeNode]
        :rtype: int
        """
        def fn(node, lo, hi):
            if not node: return hi - lo
            left = fn(node.left, lo, node.val)
            right = fn(node.right, node.val, hi)
            return min(left, right)
        return fn(root, float('-inf'), float('inf'))

정말깔끔한코드를발견했다.

가장 bst의 개념을 잘 이해하고 작성한 코드이다. 

 

 

https://leetcode.com/problems/kth-smallest-element-in-a-bst/?envType=study-plan-v2&envId=top-interview-150

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution(object):
    def kthSmallest(self, root, k):
        """
        :type root: Optional[TreeNode]
        :type k: int
        :rtype: int
        """
        def inorder_traversal(node):
            if not node:
                return []

            return inorder_traversal(node.left) + [node.val] + inorder_traversal(node.right)

        sorted_elements = inorder_traversal(root)

        return sorted_elements[k-1]

처음에 왼쪽 자식 수를 세서 센걸바탕으로 K 와 비교하고.. 그렇게 답을 찾아내는 문제일 줄 알았는데

이렇게 간단하게 풀리는 문제였다... 

다음엔 꼭 이 방법을 사용해봐야겠다...