Given a binary tree, we install cameras on the nodes of the tree. Each camera at a node can monitor its parent, itself, and its immediate children. Calculate the minimum number of cameras needed to monitor all nodes of the tree. Example 1: Input: [0,…

968. Binary Tree Cameras 思路:如果子节点只能覆盖到父节点.当前节点,但是父节点可以覆盖到他的父节点.子节点.当前节点,所以从叶子节点往上考虑 0代表子节点没有被覆盖 1代表子节点被覆盖,但是子节点没有camera 2代表子节点被覆盖,子节点有camera https://www.cnblogs.com/ethanhong/p/10200550.html /** * Definition for a binary tree node. * struct TreeNode…

作者: 负雪明烛 id: fuxuemingzhu 个人博客: http://fuxuemingzhu.cn/ 目录 题目描述 题目大意 解题方法 日期 题目地址:https://leetcode.com/problems/binary-tree-cameras/ 题目描述 Given a binary tree, we install cameras on the nodes of the tree. Each camera at a node can monitor its parent,…

Given a binary tree, we install cameras on the nodes of the tree. Each camera at a node can monitor its parent, itself, and its immediate children. Calculate the minimum number of cameras needed to monitor all nodes of the tree. Example 1: Input: [0,…

问题描述 Given a binary tree, return the inorder traversal of its nodes' values. (左 - 根 - 右) Example: Input: [1,null,2,3] 1 \ 2 / 3 Output: [1,3,2] Follow up: Recursive solution is trivial, could you do it iteratively? 参考答案 /** * Definition for a binary…

Given a binary tree, return the vertical order traversal of its nodes' values. (ie, from top to bottom, column by column). If two nodes are in the same row and column, the order should be from left to right. Examples 1: Input: [3,9,20,null,null,15,7]…

Given a binary tree where all the right nodes are either leaf nodes with a sibling (a left node that shares the same parent node) or empty, flip it upside down and turn it into a tree where the original right nodes turned into left leaf nodes. Return…

Given a binary tree, find the length of the longest consecutive sequence path. The path refers to any sequence of nodes from some starting node to any node in the tree along the parent-child connections. The longest consecutive path need to be from p…

Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level). For example:Given binary tree [3,9,20,null,null,15,7], 3 / \ 9 20 / \ 15 7 return its level order traversal as: [ [3], [9,20], [15,7…

Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left to right, level by level from leaf to root). For example:Given binary tree [3,9,20,null,null,15,7], 3 / \ 9 20 / \ 15 7 return its bottom-up level or…

Given a binary tree, return the zigzag level order traversal of its nodes' values. (ie, from left to right, then right to left for the next level and alternate between). For example:Given binary tree [3,9,20,null,null,15,7], 3 / \ 9 20 / \ 15 7 retur…

Given a binary tree, return the preorder traversal of its nodes' values. Example: Input: [1,null,2,3] 1 \ 2 / 3 Output: [1,2,3] Solution 1: # Definition for a binary tree node. # class TreeNode: # def __init__(self, x): # self.val = x # self.left = N…

Given a non-empty binary tree, find the maximum path sum. For this problem, a path is defined as any sequence of nodes from some starting node to any node in the tree along the parent-child connections. The path must contain at least one node and doe…

Given a binary tree, return all root-to-leaf paths. Note: A leaf is a node with no children. Example: Input: 1 / \ 2 3 \ 5 Output: ["1->2->5", "1->3"] Explanation: All root-to-leaf paths are: 1->2->5, 1->3 /** * Defin…

Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom. Example: Input: [1,2,3,null,5,null,4] Output: [1, 3, 4] Explanation: 1 <--- / \ 2 3 <--- \ \ 5 4 <--- S…

2019-03-27 15:39:37 问题描述: 问题求解: 很有意思的问题,问题描述简单,求解过程也可以非常的简洁,是个难得的好题. 求解的过程是自底向上进行分析,对于叶子节点,如果在叶子上放置照相机,显然是没有在其parent上放置相机来的合适的,因为叶子节点的覆盖范围没有其parent节点大. 因此,我们就可以对所有的叶子的节点的parent进行放置相机,同时将所有已经覆盖掉的节点去除掉. 对于剩下的节点重复上述的操作即可. 这里在求解的时候并不需要真实的去删除节点,只要在每个节点上加上…

1 题目 Invert a binary tree. 4 / \ 2 7 / \ / \ 1 3 6 9 to 4 / \ 7 2 / \ / \ 9 6 3 1 接口: public TreeNode invertTree(TreeNode root) 2 思路 反转一颗二叉树. 可以用递归和非递归两种方法来解. 递归的方法,写法非常简洁,五行代码搞定,交换当前左右节点,并直接调用递归即可. 非递归的方法,参考树的层序遍历,借助Queue来辅助,先把根节点排入队列中,然后从队中取出来,交换其左…

问题: Serialize and Deserialize Binary Tree 描述: Serialization is the process of converting a data structure or object into a sequence of bits so that it can be stored in a file or memory buffer, or transmitted across a network connection link to be rec…

题目描述 144. Binary Tree Preorder Traversal 94. Binary Tree Inorder Traversal 145. Binary Tree Postorder Traversal 前序排列 :根-左-右 中序排列: 左-根-右 后序排列:左-右-根 参考答案 // PreOrder /** * Definition for a binary tree node. * struct TreeNode { * int val; * TreeNode *le…

Given a binary tree, return the vertical order traversal of its nodes values. For each node at position (X, Y), its left and right children respectively will be at positions (X-1, Y-1) and (X+1, Y-1). Running a vertical line from X = -infinity to X =…

Given a binary tree with N nodes, each node has a different value from {1, ..., N}. A node in this binary tree can be flipped by swapping the left child and the right child of that node. Consider the sequence of N values reported by a preorder traver…

Given the root of a binary tree with N nodes, each node in the tree has node.val coins, and there are N coins total. In one move, we may choose two adjacent nodes and move one coin from one node to another.  (The move may be from parent to child, or…

Print a binary tree in an m*n 2D string array following these rules: The row number m should be equal to the height of the given binary tree. The column number n should always be an odd number. The root node's value (in string format) should be put i…

A binary tree is univalued if every node in the tree has the same value. Return true if and only if the given tree is univalued. 太简单了,签到题.…

Return any binary tree that matches the given preorder and postorder traversals. Values in the traversals pre and post are distinct positive integers. Example 1: Input: pre = [1,2,4,5,3,6,7], post = [4,5,2,6,7,3,1] Output: [1,2,3,4,5,6,7] Note: 1 <=…

Given a binary tree, write a function to get the maximum width of the given tree. The width of a tree is the maximum width among all levels. The binary tree has the same structure as a full binary tree, but some nodes are null. The width of one level…

Design an algorithm to encode an N-ary tree into a binary tree and decode the binary tree to get the original N-ary tree. An N-ary tree is a rooted tree in which each node has no more than N children. Similarly, a binary tree is a rooted tree in whic…

We are given a binary tree (with root node root), a target node, and an integer value K. Return a list of the values of all nodes that have a distance K from the target node.  The answer can be returned in any order. Example 1: Input: root = [3,5,1,6…

Given a binary tree, you need to compute the length of the diameter of the tree. The diameter of a binary tree is the length of the longestpath between any two nodes in a tree. This path may or may not pass through the root. Example:Given a binary tr…

Given inorder and postorder traversal of a tree, construct the binary tree. Note:You may assume that duplicates do not exist in the tree. For example, given inorder = [9,3,15,20,7] postorder = [9,15,7,20,3] Return the following binary tree: 3 / \ 9 2…