leetcode 解题思路

Acomplete binary treeis a binary tree in which every level, except possibly the last, is completely filled, and all nodes are as far left as possible.Design an algorithm to insert a new node to a complete binary tree keeping it complete after the inser..

You are given therootof abinary treewithnnodes. Each node is uniquely assigned a value from1ton. You are also given an integerstartValuerepresenting the value of the start nodes, and a different integerdestValuerepresenting the value of the d...

Given therootof a Binary Search Tree (BST), convert it to a Greater Tree such that every key of the original BST is changed to the original key plus the sum of all keys greater than the original key in BST.As a reminder, abinary search treeis a tree ...

Given therootof a binary tree, the level of its root is1, the level of its children is2, and so on.Return thesmallestlevelxsuch that the sum of all the values of nodes at levelxismaximal.Example 1:Input: root = [1,7,0,7,-8,null,null]...

Given arootof anN-ary tree, you need to compute the length of the diameter of the tree.The diameter of an N-ary tree is the length of thelongestpath between any two nodes in the tree. This path may or may not pass through the root.(Nary-Tree input...

Given therootof a binary tree, construct a0-indexedm x nstring matrixresthat represents aformatted layoutof the tree. The formatted layout matrix should be constructed using the following rules:Theheightof the tree isheightand the number of ...

Given therootof a binary tree, returnthe lowest common ancestor (LCA) of two given nodes,pandq. If either nodeporqdoes not existin the tree, returnnull. All values of the nodes in the tree areunique.According to thedefinition of LCA on Wiki...

Given a binary treeroot, a nodeXin the tree is namedgoodif in the path from root toXthere are no nodes with a valuegreater thanX.Return the number ofgoodnodes in the binary tree.Example 1:Input: root = [3,1,4,3,null,1,5]Output: 4Expla...

Given a binary tree, return thevertical ordertraversal of its nodesvalues.For each node at position(X, Y), its left and right children respectivelywill be at positions(X-1, Y-1)and(X+1, Y-1).Running a vertical line fromX = -infinitytoX = +in...

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...

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 node's key. The ...

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...

Tree的traverse，Preorder, Inorder, Postorder ，这些都是用stack来模拟考察的比较多。参考这里：PreOrder, InOrder, PostOrder 题型总结这里主要总结，divide and conquer 逻辑，往上返回result的情况；Lowest Common Ancestor of a Binary Search TreeLowest Common Ancestor of a Binary TreeClosest Binary S..

Given preorder and inorder traversal of a tree, construct the binary tree.Note:You may assume that duplicates do not exist in the tree.思路：注意current = preorder[pstart],不是preorder[0];preorder:...

Return any binary tree that matches the given preorder and postorder traversals.Values in the traversalspreandpostare distinctpositive integers.Example 1:Input: pre = [1,2,4,5,3,6,7], p...

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：inorder: left, current, right;postorder, left, ri...

Return the root node of a binarysearchtree that matches the givenpreordertraversal.(Recall that a binary search treeis a binary tree where for everynode, any descendant ofnode.lefthas a valu...

Given anodein a binary search tree, findthe in-order successor of that node in the BST.If that node has no in-order successor, returnnull.The successor of anodeis the node with the smallest key greater thannode.val.You will have direct access ...

Given a binary tree, return the postorder traversal of its nodes' values.For example:Given binary tree {1,#,2,3}, 1 \ 2 / 3return [3,2,1].Note: Recursive solution is trivi...

Given a binary tree, return the preorder traversal of its nodes' values.For example:Given binary tree {1,#,2,3}, 1 \ 2 / 3return [1,2,3].Note: Recursive solution is trivia...

Serialize and Deserialize BST思路：用preorder来构建string，因为preorder知道第一个就是root，找到后面大于root的点，就是right tree，注意null，用stringbuilder构建string。Time : O(N) serialize, O(N^2) deserialize;因为要循去找比root大的，T(n) = O(n) +...

Given a binary search tree and a node in it, find the in-order successor of that node in the BST.Note: If the given node has no in-order successor in the tree, returnnull.Example 1:Input: root...

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 co

Given two binary search treesroot1androot2.Return a list containingall the integersfromboth treessorted inascendingorder.Example 1:Input: root1 = [2,1,4], root2 = [1,0,3]Output: [0,1,1,2,3,4]思路：先用inorder traverse，把两个tree变成两个sorted queu...

Given therootof a binary tree, find the maximum valueVfor which there existsdifferentnodesAandBwhereV = |A.val - B.val|andAis an ancestor ofB.(A node A is an ancestor of B if either: any child of A is equal to B, or any child of A is an an...

Given a Binary Search Tree and a target number, return true if there exist two elements in the BST such that their sum is equal to the given target.Example 1:Input: 5 / \ 3 6 / \ \...

Given a non-empty special binary tree consisting of nodes with the non-negative value, where each node in this tree has exactlytwoorzerosub-node. If the node has two sub-nodes, then this node's va...

Given therootnode of a binary search tree, return the sum of values of all nodes with value betweenLandR(inclusive).The binary search tree is guaranteed to have unique values.Example 1:...

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 thelongestpath between any two nodes in a tree. This path may or may n...

Given a binary tree, return all duplicate subtrees. For each kind of duplicate subtrees, you only need to return the root node of anyoneof them.Two trees are duplicate if they have the same struct...

Follow up for problem "Populating Next Right Pointers in Each Node".What if the given tree could be any binary tree? Would your previous solution still work?Note:You may only use constant extr

Input: 1 \ 2 / \ 3 4Ouput:[1, 3, 4, 2]Explanation:The root doesn't have left subtree, so the root itself is left boundary.The leaves are node 3 and 4.The right boundary are no...

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Flatten a binary tree to a fake "linked list" in pre-order traversal.Here we use therightpointer in TreeNode as thenextpointer in ListNode.ExampleExample 1:Input:{1,2,5,3,4,#,6}Output：{1...

Given a non-empty binary search tree and a target value, find the value in the BST that is closest to the target.Note:Given target value is a floating point. You are guaranteed to have only on...

Given a binary tree, return all root-to-leaf paths.For example, given the following binary tree: 1 / \2 3 \ 5All root-to-leaf paths are:["1->2->5", "1->3"]思...