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原创 leetcode #92Reverse Linked List II

Reverse a linked list from position m to n. Do it in one-pass.Note: 1 ≤ m ≤ n ≤ length of list.Example:Input: 1->2->3->4->5->NULL, m = 2, n = 4Output: 1->4->3->2->5->...

2020-04-17 05:56:59 134 1

原创 leetcode #88merge sort array

Given two sorted integer arrays nums1 and nums2, merge nums2 into nums1 as one sorted array.Note:The number of elements initialized in nums1 and nums2 are m and n respectively.You may assume that n...

2020-04-16 14:17:17 94

原创 leetcode#74Search a 2D Matrix

Write an efficient algorithm that searches for a value in an m x n matrix. This matrix has the following properties:Integers in each row are sorted from left to right.The first integer of each row i...

2020-04-14 11:03:09 109

原创 leetcode#70 climbing stair

ou are climbing a stair case. It takes n steps to reach to the top.Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?Note: Given n will be a positive in...

2020-04-14 05:49:21 86

原创 leetcode#69 sqrt()

利用二分搜索，从1到x搜索if(x<=1) {return x;} int begin = 1; int end = x; int middle = 0; while(begin<=end) { middle = begin + (end - begin)/2; //不要写成middle*m...

2020-04-14 05:36:30 72

原创 leetcode #58 length of last word

Length of Last WordEasy5582203Add to ListShareGiven a string s consists of upper/lower-case alphabets and empty space characters ’ ', return the length of last word (last word means the last a...

2020-04-08 04:07:10 71

原创 leetcode 56 merge intervals

Merge IntervalsMedium3494257Add to ListShareGiven a collection of intervals, merge all overlapping intervals.Example 1:Input: [[1,3],[2,6],[8,10],[15,18]]Output: [[1,6],[8,10],[15,18]]Expl...

2020-04-08 03:38:05 77

原创 leetcode # 49 group anagrams

Given an array of strings, group anagrams together.Example:Input: [“eat”, “tea”, “tan”, “ate”, “nat”, “bat”],Output:[[“ate”,“eat”,“tea”],[“nat”,“tan”],[“bat”]]Note:All inputs will be in lowe...

2020-04-04 02:54:22 78

原创 leetcode#49. Group Anagrams

Given an array of strings, group anagrams together.Example:Input: [“eat”, “tea”, “tan”, “ate”, “nat”, “bat”],Output:[[“ate”,“eat”,“tea”],[“nat”,“tan”],[“bat”]]Note:All inputs will be in lowe...

2020-04-04 02:16:56 66

原创 leetcode 48 # rotate image

You are given an n x n 2D matrix representing an image.Rotate the image by 90 degrees (clockwise).Note:You have to rotate the image in-place, which means you have to modify the input 2D matrix dire...

2020-04-03 04:39:10 64

原创 leetcode #43 Multiply Strings

Given two non-negative integers num1 and num2 represented as strings, return the product of num1 and num2, also represented as a string.Example 1:Input: num1 = “2”, num2 = “3”Output: “6”Example 2:...

2020-04-03 03:20:35 82

原创 leetcode回溯法总结

第二遍做leetcode 中的回溯法，发现不光没有更好的理解，甚至遗忘了很多。所以今天觉得做一篇有关回溯法的总结首先，回溯法的基本思想：从一条路往前走，能进则进，不能进则退回，换一条路再试回溯法的基本定义和概念首先要明确下面三个概念1约束函数：约束函数是根据题意定出，通过描述合法解的一般特征用于去除不合法的解，从而避免继续搜索出这个不合法解的剩余部分2状态空间树状态空间树是一个对...

2020-04-02 04:14:49 152

原创 leetcode#33. Search in Rotated Sorted Array

Suppose an array sorted in ascending order 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]).You are given a target value to search. If found in...

2020-03-26 06:50:04 59

原创 leetcode #26 Remove Duplicates from Sorted Array

Given a sorted array nums, remove the duplicates in-place such that each element appear only once and return the new length.Do not allocate extra space for another array, you must do this by modifyin...

2020-03-24 06:47:52 77

原创 Leetcode #24. Swap Nodes in Pairs java

Given a linked list, swap every two adjacent nodes and return its head.You may not modify the values in the list’s nodes, only nodes itself may be changed.Example:Given 1->2->3->4, you sho...

2020-03-24 06:23:59 63

原创 leetcode #17. Letter Combinations of a Phone Number

Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent.A mapping of digit to letters (just like on the telephone buttons) is give...

2020-03-20 09:01:55 81

原创 leetcode#14. Longest Common Prefix

Write a function to find the longest common prefix string amongst an array of strings.If there is no common prefix, return an empty string “”.Example 1:Input: [“flower”,“flow”,“flight”]Output: “fl...

2020-03-18 13:02:06 87

原创 leetcode#150. Evaluate Reverse Polish Notation

Evaluate the value of an arithmetic expression in Reverse Polish Notation.Valid operators are +, -, *, /. Each operand may be an integer or another expression.Note:Division between two integers sho...

2020-03-07 10:48:49 54

原创 #148. Sort List

Sort a linked list in O(n log n) time using constant space complexity.Example 1:Input: 4->2->1->3Output: 1->2->3->4Example 2:Input: -1->5->3->4->0Output: -1->0-&...

2020-03-07 05:57:07 61

原创 leetcode #147. Insertion Sort List

Sort a linked list using insertion sort.A graphical example of insertion sort. The partial sorted list (black) initially contains only the first element in the list.With each iteration one element (...

2020-03-06 14:49:19 83

原创 leetcode #143. Reorder List

Given a singly linked list L: L0→L1→…→Ln-1→Ln,reorder it to: L0→Ln→L1→Ln-1→L2→Ln-2→…You may not modify the values in the list’s nodes, only nodes itself may be changed.Example 1:Given 1->2->...

2020-03-06 04:02:44 66

原创 leetcode#142. Linked List Cycle II

Given a linked list, return the node where the cycle begins. If there is no cycle, return null.To represent a cycle in the given linked list, we use an integer pos which represents the position (0-in...

2020-03-05 08:08:23 64

原创 leetcode #141. Linked List Cycle

Given a linked list, determine if it has a cycle in it.To represent a cycle in the given linked list, we use an integer pos which represents the position (0-indexed) in the linked list where tail con...

2020-03-05 06:52:13 58

原创 leetcode #138. Copy List with Random Pointer

A linked list is given such that each node contains an additional random pointer which could point to any node in the list or null.Return a deep copy of the list.The Linked List is represented in th...

2020-03-05 04:14:26 117

原创 leetcode #136. Single Number

Given a non-empty 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 usin...

2020-03-04 13:55:31 69

原创 leetcode #134. Gas Station

There are N gas stations along a circular route, where the amount of gas at station i is gas[i].You have a car with an unlimited gas tank and it costs cost[i] of gas to travel from station i to its n...

2020-03-04 12:31:50 156

原创 leetcode #131 Palindrome Partitioning

Given a string s, partition s such that every substring of the partition is a palindrome.Return all possible palindrome partitioning of s.Example:Input: “aab”Output:[[“aa”,“b”],[“a”,“a”,“b”]]...

2020-03-04 12:01:58 78

原创 leetcode #122. Best Time to Buy and Sell Stock II

Say you have an array for which the ith element is the price of a given stock on day i.Design an algorithm to find the maximum profit. You may complete as many transactions as you like (i.e., buy one...

2020-03-04 04:30:15 65

原创 letcode#119. Pascal's Triangle II

Given a non-negative index k where k ≤ 33, return the kth index row of the Pascal’s triangle.Note that the row index starts from 0.In Pascal’s triangle, each number is the sum of the two numbers dir...

2020-03-03 07:36:29 54

原创 leetcode#116 Populating Next Right Pointers in Each Node

You are given a perfect binary tree where all leaves are on the same level, and every parent has two children. The binary tree has the following definition:struct Node {int val;Node *left;Node *ri...

2020-02-29 05:25:42 70

原创 leetcode #114. Flatten Binary Tree to Linked List

Given a binary tree, flatten it to a linked list in-place.For example, given the following tree:1/ 2 5/ \ 3 4 6The flattened tree should look like:123456知识点stack 先进先出pop ...

2020-02-28 13:49:42 72

原创 leetcode#113. Path Sum II

Given a binary tree and a sum, find all root-to-leaf paths where each path’s sum equals the given sum.Note: A leaf is a node with no children.Example:Given the below binary tree and sum = 22, 5 ...

2020-02-28 04:19:27 79

原创 leetcode #111. Minimum Depth of Binary Tree

Given a binary tree, find its minimum depth.The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.Note: A leaf is a node with no children....

2020-02-27 07:45:25 77

原创 leetcode#110. Balanced Binary Tree

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 left and right subtrees of every node differ in heigh...

2020-02-27 06:48:14 76

原创 leetcode#109. Convert Sorted List to Binary Search Tree

Given a singly linked list where elements are sorted in ascending order, convert it to a height balanced BST.For this problem, a height-balanced binary tree is defined as a binary tree in which the d...

2020-02-26 13:47:17 54

原创 leetcode#108. Convert Sorted Array to Binary Search Tree

二分查找中的问题循环条件为什么不是 (l<r)第一，如果数组长度为1的话，不管查找什么都会恒定的返回-1，这显然是错的。第二，当l + 1 = r的时候，mid=l，如果此时A[mid]小于target执行l=mid+1=r，再次循环时候while条件不满足，将退出循环，但是A[right]可能==target。考虑[3,5] k=5的情况，这时候会返nick大神讲解看了视频发现了...

2020-02-26 07:45:08 82

原创 leetcode#102Binary Tree Level Order Traversal

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 7retu...

2020-02-26 06:34:22 55

原创 leetcode #107. Binary Tree Level Order Traversal II

Binary Tree Level Order Traversal IIEasy1039186Add to ListShareGiven a binary tree, return the bottom-up level order traversal of its nodes’ values. (ie, from left to right, level by level fro...

2020-02-26 06:33:46 104

原创 leetcode#105 Construct Binary Tree from Preorder and Inorder Traversal

Given preorder and inorder traversal of a tree, construct the binary tree.Note:You may assume that duplicates do not exist in the tree.For example, givenpreorder = [3,9,20,15,7]inorder = [9,3,15,...

2020-02-26 06:00:38 52

原创 leetcode #79. Word Search

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 horizontally or vertically ne...

2020-02-26 05:25:46 76

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