ljffdream的专栏

leetcode

【题目】Given inorder and postorder traversal of a tree, construct the binary tree.Note:You may assume that duplicates do not exist in the tree.【思路】pretty similar with that

【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

【题目】Given a binary tree, determine if it is a valid binary search tree (BST).Assume a BST is defined as follows:The left subtree of a node contains only nodes with keys less than the nod

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

【题目】Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.For example:Given the below binary tree and sum = 22, 5

[题目]Given two words (beginWord and endWord), and a dictionary, find the length ofshortest transformation sequence frombeginWord to endWord, such that:Only one letter can be changed at a ti

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

【题目】Given a binary tree, return the inorder traversal of its nodes' values.For example:Given binary tree {1,#,2,3}, 1 \ 2 / 3return [1,3,2].Note: Recursi

【树的定义】public class TreeNode{int val;TreeNode left;TreeNode right;TreeNode(int x){val=x;}}【前序遍历】递归：public void preOrder(TreeNodebiTree){System.out.printf(biTree.val+"");TreeNode leftTr

morris traversal 原理很简单，利用所有叶子结点的right 指针，指向其后继结点，组成一个环，在第二次遍历到这个结点时，由于其左子树已经遍历完了，则访问该结点如下图为morris 的一个示例【morris中序遍历】void bst_morris_inorder(struct bst_node *root){ struct bst_n

【题目】Given n, how many structurally unique BST's (binary search trees) that store values 1...n?For example,Given n = 3, there are a total of 5 unique BST's. 1 3 3 2

【题目】Given a singly linked list where elements are sorted in ascending order, convert it to a height balanced BST.【思路】这道题目就和array不一样，因为是linkedlist所以，不能随意访问到中间的元素，那么就只能一步一步从头开始顺序访问，从列表到BST,我们能感受到构

【题目】Given preorder and inorder traversal of a tree, construct the binary tree.【思路】Hint:A good way to attempt this question is to work backwards. Approach this question by drawing a binary