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摘要： Givenn, how many structurally uniqueBST's(binary search trees) that store values 1...n?For example,Givenn= 3, there are a total of 5 unique BST's. 1 3 3 2 1 \ / / / \ \ 3 2 1 1 3 2 / / \ \ 2 1 ... 阅读全文

摘要： Given an unsorted array of integers, find the length of the longest consecutive elements sequence.For example,Given[100, 4, 200, 1, 3, 2],The longest consecutive elements sequence is[1, 2, 3, 4]. Return its length:4.Your algorithm should run in O(n) complexity.Summary: The key idea is using hash map 阅读全文

摘要： Given a linked list, remove thenthnode from the end of list and return its head.For example, Given linked list: 1->2->3->4->5, and n = 2. After removing the second node from the end, the linked list becomes 1->2->3->5.Note:Givennwill always be valid.Try to do this in one pass.Su 阅读全文

摘要： The string"PAYPALISHIRING"is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)P A H NA P L S I I GY I RAnd then read line by line:"PAHNAPLSIIGYIR"Write the code that will take a string and 阅读全文

摘要： Write a program to solve a Sudoku puzzle by filling the empty cells.Empty cells are indicated by the character'.'.You may assume that there will be only one unique solution.A sudoku puzzle......and its solution numbers marked in red.Summary: finds the cell which has the least candidates firs 阅读全文

摘要： Given a binary tree struct TreeLinkNode { TreeLinkNode *left; TreeLinkNode *right; TreeLinkNode *next; }Populate each next pointer to point to its next right node. If there is no next right node, the next pointer should be set toNULL.Initially, all next pointers are set toNULL.N... 阅读全文

摘要： Given a binary tree, return thelevel ordertraversal of its nodes' values. (ie, from left to right, level by level).For example:Given binary tree{3,9,20,#,#,15,7}, 3 / \ 9 20 / \ 15 7return its level order traversal as:[ [3], [9,20], [15,7]]Solution: 1 vector > levelOrder(TreeNo... 阅读全文

摘要： Clone an undirected graph. Each node in the graph contains alabeland a list of itsneighbors.OJ's undirected graph serialization:Nodes are labeled uniquely.We use#as a separator for each node, and,as a separator for node label and each neighbor of the node.As an example, consider the serialized g 阅读全文

摘要： Mergeksorted linked lists and return it as one sorted list. Analyze and describe its complexity.Summary: Finds the smallest node every round, then links it to the one sorted list. 1 ListNode *mergeKLists(vector &lists) { 2 ListNode * head = NULL; 3 ListNode * pre_node = NULL; 4 ... 阅读全文

摘要： Given two integersnandk, return all possible combinations ofknumbers out of 1 ...n.For example,Ifn= 4 andk= 2, a solution is:[ [2,4], [3,4], [2,3], [1,2], [1,3], [1,4],]Summary: recursive functions 1 class Solution { 2 public: 3 vector > combine(int n, int k) { 4 vector > combinati... 阅读全文