代码随想录算法训练营day18 |530.二叉搜索树的最小绝对差 501.二叉搜索树中的众数 236. 二叉树的最近公共祖先

学习资料：https://programmercarl.com/0530.二叉搜索树的最小绝对差.html

530.二叉搜索树的最小绝对差（双指针法，pre&cur，设置最小差值初始为无穷大，当差值<最小差值就更新最小差值）

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# 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 __init__(self):self.result = float('inf')  # 设置最小值的初值为无穷大self.pre = Nonedef getMinimumDifference(self, root):""":type root: TreeNode:rtype: int"""if root is None:returnself.getMinimumDifference(root.left)# 因为中序遍历，这里root.val肯定大于self.pre.valif self.pre is not None:self.result = min(self.result, root.val-self.pre.val) self.pre = rootself.getMinimumDifference(root.right)return self.result

501.二叉搜索树中的众数（加两个函数,init & searchBST；双指针，当pre.val==cur.val，count+=1）

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# 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 __init__(self):self.result = []self.pre = Noneself.count = 0self.maxCount = 0def searchBST(self, cur):if cur is None:returnself.searchBST(cur.left)if self.pre is None:self.count = 1elif self.pre.val == cur.val:self.count += 1else:self.count = 1self.pre = curif self.count == self.maxCount:self.result.append(cur.val)if self.count > self.maxCount:self.maxCount = self.countself.result = [cur.val]self.searchBST(cur.right)returndef findMode(self, root):""":type root: TreeNode:rtype: List[int]"""self.count = 0self.maxCount = 0self.pre = Noneself.result = []self.searchBST(root)return self.result

236.二叉树的最近公共祖先（看代码简单，但是想不通；递归；左右中：后序遍历）

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# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = Noneclass Solution(object):def lowestCommonAncestor(self, root, p, q):""":type root: TreeNode:type p: TreeNode:type q: TreeNode:rtype: TreeNode"""if root == q or root == p or root is None:return rootleft = self.lowestCommonAncestor(root.left, p, q)right = self.lowestCommonAncestor(root.right, p, q)if left is not None and right is not None:return rootif left is None and right is not None:return rightelif left is not None and right is None:return leftelse:return None

PS:今天的后两道题没看懂，先抄一下
延迟了一天，因为昨晚有今年最大的月亮又恰逢难得的晴天，看到了月球超级靓但是还是差点意思没看到凹，不过第一次看到土星，好远好小好棒，还有环，就是没注意颜色
昨天还吃了美味寿司，一个人干了两大碟，有实力儿
破公司的秋招，把人当猴耍