ljffdream的专栏

[题目] Invert a binary tree. 4 / \ 2 7 / \ / \ 1 3 6 9 to 4 / \ 7 2 / \ / \ 9 6 3 1 Trivia: This problem was inspired by this original tweet by

[题目] [思路] BST的特点就是排序性，左边的节点一定比root小，右边的节点一定比root大。 另外就是二分性。 找第k个，可以先看左边树节点的个数，小于k的话，就保证了肯定是在右边。那么去找右边的k-left. k - left,就变成了新的k. 数root所在的树的节点数。这个就是用递归实现。想法就是，如果root自己本身就是null,那么就return 0; 否则至

【题目】 Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST. According to the definition of LCA on Wikipedia: “The lowest common ancestor is defi