ljffdream的专栏

【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 list, rotate the list to the right by k places, where k is non-negative.For example:Given 1->2->3->4->5->NULL and k = 2,return 4->5->1->2->3->NULL.【思路】实质就是n-k个元素挪到了链子的前面， 第

【题目】Find the kth largest element in an unsorted array. Note that it is the kth largest element in the sorted order, not the kth distinct element.For example,Given [3,2,1,5,6,4] and k = 2, retu

【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】【分析】首先，先sort,如果target > 0:【代码】using recursive 这恐怕的 O(n2)...过程：before recursion : [2]before recursion : [2, 2]before recursion : [2, 2, 2]after recursion and remove :

【题目】【思路】The problem can be simply broken down as two binary searches for the begining and end of the range, respectively:First let's find the left boundary of the range. We ini

【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】【思路】First of all, allow me to explain the meaning of strict O(1) auxiliary space complexity.It means the maximum number of memory used by the program, except the memory taken by th

【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】You are given an n x n 2D matrix representing an image.Rotate the image by 90 degrees (clockwise).【思路】The idea was firstly transpose the matrix and then flip it symmetrically.

【题目】Given a singly linked list L: L0→L1→…→Ln-1→Ln,reorder it to: L0→Ln→L1→Ln-1→L2→Ln-2→…You must do this in-place without altering the nodes' values.For example,Given {1,2,3,4}, reorder it

[timu]Given a 2D board and a word, find if the word exists in the grid.The word can be constructed from letters of sequentially adjacent cell, where "adjacent" cells are those horizontal

【题目】Given a triangle, find the minimum path sum from top to bottom. Each step you may move to adjacent numbers on the row below.For example, given the following triangle[ [2], [

【题目】Given a collection of integers thatmight contain duplicates, nums,return all possible subsets.Note:Elements in a subset must be in non-descending order.The solution set must not contai

【题目】Given a string S, find the longest palindromic substring in S. You may assume that the maximum length of S is 1000, and there exists one unique longest palindromic substring.【思路】中心检测

【题目】【思路】My idea is simple: store states of each row in the first of that row, and store states of each column in the first of that column. Because the state of row0 and the state of column0

[timu]Search a 2D MatrixTotal Accepted: 52191 Total Submissions: 164580Write an efficient algorithm that searches for a value in an m x n matrix. This matrix has the followin

【题目】Given a m x n grid filled with non-negative numbers, find a path from top left to bottom right which minimizes the sum of all numbers along its path.Note: You can only move either down

【题目】Follow up for "Unique Paths":Now consider if some obstacles are added to the grids. How many unique paths would there be?An obstacle and empty space is marked as 1 and 0 respectively

【题目】Given aninteger n,generate a square matrix filled with elements from 1 to n2 inspiral order.For example,Given n = 3,Youshould return the following matrix:[  [ 1, 2, 3 ],  [ 8, 9, 4 ]

[timu] Given an array with n objects colored red, white or blue, sort them so that objects of the same color are adja

【题目】Given a set of distinct integers, nums, return all possible subsets.Note:Elements in a subset must be in non-descending order.The solution set must not contain duplicate subsets.

[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】Given a linked list and a value x, partition it such that all nodes less than x come before nodes greater than or equal to x.You should preserve the original relative order of the nodes

【题目】Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.For example, given n = 3, a solution set is:"((()))", "(()())", "(())()", "()((

【题目】Given an array with n objects colored red, white or blue, sort them so that objects of the same color are adjacent, with the colors in the order red, white and blue.Here, we will use the

【题目】Find the contiguous subarray within an array (containing at least one number) which has the largest sum.For example, given the array [−2,1,−3,4,−1,2,1,−5,4],the contiguous subarray [4,

【题目】Given an array of integers, every element appears twice except for one. Find that single one.Note:Your algorithm should have a linear runtime complexity. Could you implement it without u

【题目】A robot is located at the top-left corner of a m x n grid (marked 'Start' in the diagram below).The robot can only move either down or right at any point in time. The robot is trying to

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【题目】Given an input string, reverse the string word by word.For example,Given s = "the sky is blue",return "blue is sky the".click to show clarification.Clarification:What con

【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】The gray code is a binary numeral system where two successive values differ in only one bit.Given a non-negative integer n representing the total number of bits in the code, print the se

【题目】Given an integer, convert it to a roman numeral.Input is guaranteed to be within the range from 1 to 3999.【分析】只要是遵守那个转换规则就好吧。然后就是数学处理。【代码1】private static LinkedHashMap numToRoman

【题目】Given a linked list, swap every two adjacent nodes and return its head.For example,Given 1->2->3->4, you should return the list as 2->1->4->3.Your algorithm should use only constant

【题目】Suppose a sorted array is rotated at some pivot unknown to you beforehand.(i.e., 0 1 2 4 5 6 7 might become 4 5 6 7 0 1 2).Find the minimum element.You may assume no duplicate

[题目] medianFollow up for "Search in Rotated Sorted Array":What if duplicates are allowed?Would this affect the run-time complexity? How and why?Write a function to determine if a given tar

[题目]Note: This is an extension of House Robber.After robbing those houses on that street, the thief has found himself a new place for his thievery so that he will not get too much attention. T

[题目]Given a 2d grid map of '1's (land) and '0's (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You ma