leetcode 解题思路

You are given some lists ofregionswhere the first region of each list includes all other regions in that list.Naturally, if a regionxcontains another regionythenxis bigger thany. Also, by definition, a regionxcontains itself.Given two region...

Given four integers sx, sy, tx, and ty, return true if it is possible to convert the point (sx, sy) to the point (tx, ty) through some operations, or false otherwise.The allowed operation on some point (x, y) is to convert it to either (x, x + y) or (x +

One way to serialize a binary tree is to usepreorder traversal. When we encounter a non-null node, we record the node's value. If it is a null node, we record using a sentinel value such as'#'.For example, the above binary tree can be serialized to t..

Given two nodes of abinary treepandq, returntheirlowest common ancestor (LCA).Each node will have a reference to its parent node. The definition forNodeis below:class Node { public int val; public Node left; public Node right; ...

Given the root of a Binary Search Tree (BST), return the minimum difference between the values of any two different nodes in the tree.Example 1:Input: root = [4,2,6,1,3]Output: 1Example 2:Input: root = [1,0,48,null,null,12,49]Output: 1Constraints:

Given a binary search tree, return abalancedbinary search tree with the same node values.A binary search tree isbalancedif and only ifthe depth of the two subtrees ofeverynode never differ by more than 1.If there is more than one answer, return ...

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 therootof a binary tree withNnodes, eachnodein the tree hasnode.valcoins, and there areNcoins 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 from ...

Given an integer array with no duplicates. A maximum tree building on this array is defined as follow:The root is the maximum number in the array. The left subtree is the maximum tree constructed f...

Input:root = [1,2,3,4,null,null,null,5,null,6], k = 2Diagram of binary tree: 1 / \ 2 3 / 4 / 5 / 6Output: 3Expl...

Lowest Common Ancestor of a Binary Search TreeGiven 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 Wikipedi...

Given a rooted binary tree, return the lowest common ancestor of its deepest leaves.Recall that:The node of a binary tree is aleafif and only if it has no children Thedepthof the root of the ...

Path Sum IGiven a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.Note:A leaf is a node with no childre...

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...

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 a binary search tree and a node in it, find the in-order predecessor of that node in the BST.ExampleExample1Input: root = {2,1,3}, p = 1Output: nullExample2Input: root = {2,1}, p =...

Given the root and two nodes in a Binary Tree. Find the lowest common ancestor(LCA) of the two nodes.The lowest common ancestor is the node with largest depth which is the ancestor of both nodes.T...

Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.For example:Given the below binary tree and sum =...

Given an array of numbers, verify whether it is the correct preorder traversal sequence of a binary search tree.You may assume each number in the sequence is unique.Follow up:Could you do it usi

You are given a binary tree in which each node contains an integer value.Find the number of paths that sum to a given value.The path does not need to start or end at the root or a leaf, but it ...

Given a root node reference of a BST and a key, delete the node with the given key in the BST. Return the root node reference (possibly updated) of the BST.Basically, the deletion can be divided ...

Given a binary tree, collect a tree's nodes as if you were doing this: Collect and remove all leaves, repeat until the tree is empty.Example:Given binary tree 1 / \ ...

Given a binary tree, find its maximum depth.The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.思路1： traverse的方法，就是访问所有的点，然后记录一些信息，从而最...

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 ...

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...

Implement an iterator over a binary search tree (BST). Your iterator will be initialized with the root node of a BST.Calling next() will return the next smallest number in the BST.Note: next() ...

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 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 non-empty binary tree, return the average value of the nodes on each level in the form of an array.Example 1:Input: 3 / \ 9 20 / \ 15 7Output: [3, 14.5, 11]Explanati...

Given two binary trees and imagine that when you put one of them to cover the other, some nodes of the two trees are overlapped while the others are not.You need to merge them into a new binary tree...

 Find the sum of all left leaves in a given binary tree.Example: 3 / \ 9 20 / \ 15 7There are two left leaves in the binary tree, with values 9 and 15 respectively. Return ...

Given a binary search tree and the lowest and highest boundaries as L and R, trim the tree so that all its elements lies in [L, R] (R >= L). You might need to change the root of the tree, so the re...

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 defined betwee...

Given a binary tree, find the largest subtree which is a Binary Search Tree (BST), where largest means subtree with largest number of nodes in it.Note:A subtree must include all of its descendan

Givenn, generate all structurally uniqueBST's(binary search trees) that store values 1...n.For example,Givenn= 3, your program should return all 5 unique BST's shown below. 1 3

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: Recursive solution is trivial...

Two elements of a binary search tree (BST) are swapped by mistake.Recover the tree without changing its structure.Note:A solution using O(n) space is pretty straight forward. Could you devise a

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 an array where elements are sorted in ascending order, convert it to a height balanced BST.思路：找中间点，就是root，然后两边分别构造左子树和右子树。/** * Definition for a binary tree node. * public class TreeNode ...

Given a binary tree, determine if it is height-balanced.For this problem, a height-balanced binary tree is defined as:a binary tree in which the depth of the two subtrees ofeverynode never diff...