whiterbear的专栏

Given two words (beginWord and endWord), and a dictionary's word list, find all shortest transformation sequence(s) from beginWord to endWord, such that:Only one letter can be changed at a time Eac...

Given two words (beginWord and endWord), and a dictionary's word list, find the length of shortest transformation sequence from beginWord to endWord, such that:Only one letter can be changed at a ti...

Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in-place.Example 1:Input: [  [1,1,1],  [1,0,1],  [1,1,1]]Output: [  [1,0,1],  [0,0,0],  [1,0,1]]E...

Implement int sqrt(int x).Compute and return the square root of x, where x is guaranteed to be a non-negative integer.Since the return type is an integer, the decimal digits are truncated and only...

Bitwise AND of Numbers RangeGiven a range [m, n] where 0 For example, given the range [5, 7], you should return 4.分析：给定m和n，返回m到n闭区间内所有元素位运算&后的结果。我们知道a和b进行And操作时，在a和b同时为1的时候结果才为1.

整理一下LeetCode上三道与栈有关的题，分别是Implement Queue using Stacks，Implement Stack using Queues和Min Stack。1.Implement Queue using StacksImplement the following operations of a queue using stacks.

Peeking IteratorGiven an Iterator class interface with methods: next() and hasNext(), design and implement a PeekingIterator that support the peek() operation -- it essentially peek() at the

Excel Sheet Column TitleGiven a positive integer, return its corresponding column title as appear in an Excel sheet.For example: 1 -> A 2 -> B 3 -> C ... 26 -> Z 27

4SumGiven an array S of n integers, are there elements a, b, c, and d in S such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target.Note:

3Sum Closest Given an array S of n integers, find three integers in S such that the sum is closest to a given number, target. Return the sum of the three integers. You may assume that each i

3SumGiven an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.Note:Elements in a tr

Lowest Common Ancestor of a Binary TreeGiven 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 lowes

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 Wiki

Remove Nth Node From End of ListGiven a linked list, remove the nth node from the end of list and return its head.For example, Given linked list: 1->2->3->4->5, and n = 2. After re

Maximum Product SubarrayFind the contiguous subarray within an array (containing at least one number) which has the largest product.For example, given the array [2,3,-2,4],the contiguous

Product of Array Except SelfGiven an array of n integers where n > 1, nums, return an array output such that output[i] is equal to the product of all the elements of nums except nums[i].

Isomorphic StringsGiven two strings s and t, determine if they are isomorphic.Two strings are isomorphic if the characters in s can be replaced to get t.All occurrences of a character

Insertion Sort ListSort a linked list using insertion sort.原题链接为:https://leetcode.com/problems/insertion-sort-list分析：使用插入排序对链表进行排序。可以新建一个带头节点的有序链表，每次从原链表中选择一个节点，插入到带头节点的链表中。C++代码：...

Sort ListSort a linked list in O(n log n) time using constant space complexity.分析：给链表排序，要求O(nlogn)的时间，O(1)的空间。链表不是数组，给它排序不能像数组一样可以通过各种下标操作。能够想到的方法也就是（1）通过新建一个有序链表，每次从原来链表中选择一个元素到新的有序

Happy NumberWrite an algorithm to determine if a number is "happy".A happy number is a number defined by the following process: Starting with any positive integer, replace the number by th

Remove Duplicates from Sorted ArrayGiven a sorted array, remove the duplicates in place such that each element appear only once and return the new length.Do not allocate extra space for an

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

Sort Colors 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

First Missing PositiveGiven an unsorted integer array, find the first missing positive integer.For example,Given [1,2,0] return 3,and [3,4,-1,1] return 2.Your algorithm should run

Merge k Sorted ListsMerge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity.分析1：利用上一道题（合并两个有序链表）代码，进行两两合并，最后得到一个链表。代码如下，然而一直超时。超时的代码：

Merge Two Sorted Lists Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.分析：合并两个有序的链表。

Merge Sorted Array Given two sorted integer arrays nums1 and nums2, merge nums2 into nums1 as one sorted array.Note:You may assume that nums1 has enough space (size that is greater or

Search a 2D Matrix IIWrite 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 in ascending fr

Search Insert PositionGiven a sorted array and a target value, return the index if the target is found. If not, return the index where it would be if it were inserted in order.You may assu

Search for a Range Given a sorted array of integers, find the starting and ending position of a given target value.Your algorithm's runtime complexity must be in the order of O(log n).

Integer to RomanGiven an integer, convert it to a roman numeral.Input is guaranteed to be within the range from 1 to 3999.分析：Roman to Integer的逆转换，逆着来，难度比上一道题难了一些。问题的核心是如何处理一些数比如40，90，900

Roman to Integer Given a roman numeral, convert it to an integer.Input is guaranteed to be within the range from 1 to 3999.分析：给定罗马字符串，输出该串对应的十进制阿拉伯数。首先我们要了解罗马数字的表示规则。从百科上我找到了：

String to Integer (atoi)注：要开始研究僧生活了，希望能在这一年里多编码，努力提高编程水平，提高算法水平。题目链接：https://leetcode.com/problems/string-to-integer-atoi/#Implement atoi to convert a str

Remove ElementGiven an array and a value, remove all instances of that value in place and return the new length.The order of elements can be changed. It doesn't matter what you leave beyon

House RobberYou are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed, the only constraint stopping you from robbing each of them is t

House Robber IINote: 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 to

Climbing StairsYou 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?分析：

TriangleGiven 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],

Perfect SquaresGiven a positive integer n, find the least number of perfect square numbers (for example, 1, 4, 9, 16, ...) which sum to n.For example, given n = 12, return 3 because 12

Longest Valid ParenthesesGiven a string containing just the characters '(' and ')', find the length of the longest valid (well-formed) parentheses substring.For "(()", the longest va