2014 年 5月随笔档案 - neverlandly

Leetcode: Triangle

摘要：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 fol... 阅读全文

posted @ 2014-05-29 23:57 neverlandly 阅读(270) 评论(0) 推荐(0) 编辑

Leetcode: Best Time to Buy and Sell Stock II

摘要：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 complet... 阅读全文

posted @ 2014-05-29 04:03 neverlandly 阅读(264) 评论(0) 推荐(0) 编辑

Leetcode: Best Time to Buy and Sell Stock

摘要：这道题求进行一次交易能得到的最大利润。如果用brute force的解法就是对每组交易都看一下利润，取其中最大的，总用有n*(n-1)/2个可能交易，所以复杂度是O(n^2)。跟Maximum Subarray非常类似，用“局部最优和全局最优解法”。思路是维护两个变量，一个是到目前为止最好的交易，另阅读全文

posted @ 2014-05-29 03:37 neverlandly 阅读(375) 评论(0) 推荐(0) 编辑

Leetcode: Pascal's Triangle II

摘要：Given an index k, return the kth row of the Pascal's triangle.For example, given k = 3,Return [1,3,3,1].Note:Could you optimize your algorithm to use ... 阅读全文

posted @ 2014-05-28 05:44 neverlandly 阅读(410) 评论(0) 推荐(0) 编辑

Leetcode: Pascal's Triangle

摘要：Given numRows, generate the first numRows of Pascal's triangle.For example, given numRows = 5,Return[ [1], [1,1], [1,2,1], [1,3,3,1], [1,4,6... 阅读全文

posted @ 2014-05-28 04:29 neverlandly 阅读(229) 评论(0) 推荐(0) 编辑

Leetcode: Path Sum II

摘要：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 su 阅读全文

posted @ 2014-05-23 06:14 neverlandly 阅读(456) 评论(0) 推荐(0) 编辑

Leetcode: Convert Sorted Array to Binary Search Tree

摘要：Given an array where elements are sorted in ascending order, convert it to a height balanced BST.基本上一次过，要注意边界条件的问题：如果在recursion里有两个参数int begin, end, 递... 阅读全文

posted @ 2014-05-23 03:39 neverlandly 阅读(293) 评论(0) 推荐(0) 编辑

Leetcode: Merge Sorted Array

摘要：Given two sorted integer arrays A and B, merge B into A as one sorted array.Note:You may assume that A has enough space (size that is greater or equal... 阅读全文

posted @ 2014-05-23 02:56 neverlandly 阅读(256) 评论(0) 推荐(0) 编辑

Leetcode: Word Search

摘要：Remember to change the character back after loop through all the possibility 非常聪明的方法1：O（1）空间的话可以不用visited数组，直接改board。改了之后，再访问的时候因为board[i][j] != word. 阅读全文

posted @ 2014-05-22 23:45 neverlandly 阅读(652) 评论(0) 推荐(0) 编辑

Leetcode: Remove Duplicates from Sorted Array II

摘要：Follow up for "Remove Duplicates": What if duplicates are allowed at most twice? For example, Given sorted array A = [1,1,1,2,2,3], Your function shou 阅读全文

posted @ 2014-05-21 12:33 neverlandly 阅读(241) 评论(0) 推荐(0) 编辑

Leetcode: Subsets

摘要：Adopted approach: Notice that in line 11, you should create a copy of current path, and add it to res. Otherwise, it'll be edited later, and be wiped 阅读全文

posted @ 2014-05-21 12:25 neverlandly 阅读(563) 评论(1) 推荐(0) 编辑

Leetcode: Combinations

摘要：Given two integers n and k, return all possible combinations of k numbers out of 1 ... n.For example,If n = 4 and k = 2, a solution is:[ [2,4], [3,4... 阅读全文

posted @ 2014-05-21 05:54 neverlandly 阅读(320) 评论(0) 推荐(0) 编辑

Leetcode: Climbing Stairs

摘要：这道题目是求跑楼梯的可行解法数量。每一步可以爬一格或者两个楼梯，可以发现，递推式是f(n)=f(n-1)+f(n-2)，也就是等于前一格的可行数量加上前两格的可行数量。熟悉的朋友可能发现了，这个递归式正是斐波那契数列的定义. 这里base case 是f(1)=1, f(2)=2. Fibonacc 阅读全文

posted @ 2014-05-20 07:10 neverlandly 阅读(369) 评论(0) 推荐(0) 编辑

Leetcode: Set Matrix Zeroes

摘要：一次过，空间复杂度为O(m+n), 下一次做的时候寻找constant space solution。用boolean array也可以，用bit vector可能会更节省. 其实还可以再优化，我们考虑使用第一行和第一列来记录上面所说的行和列的置0情况，这里问题是那么第一行和第一列自己怎么办？想要记阅读全文

posted @ 2014-05-20 07:08 neverlandly 阅读(299) 评论(0) 推荐(0) 编辑

Leetcode: Search a 2D Matrix

摘要：1 Write an efficient algorithm that searches for a value in an m x n matrix. This matrix has the following properties: 2 3 Integers in each row are ... 阅读全文

posted @ 2014-05-20 06:56 neverlandly 阅读(349) 评论(0) 推荐(0) 编辑

Leetcode: Add Binary

摘要：Given two binary strings, return their sum (also a binary string).For example,a = "11"b = "1"Return "100".我自己的做法：用StringBuffer, a和b都从末尾扫描到开头，而StringBu... 阅读全文

posted @ 2014-05-14 11:26 neverlandly 阅读(230) 评论(0) 推荐(0) 编辑

Leetcode: Unique Paths

摘要：推荐方法：DP矩阵做法其实还可以节省一维：2D矩阵变成一维数组DP：一维DP方法2：阅读全文

posted @ 2014-05-14 06:01 neverlandly 阅读(362) 评论(0) 推荐(0) 编辑

Leetcode: Trapping Rain Water

摘要：这道题做的比较艰辛，一开始自己想的是一个用stack的解法，感觉过于繁琐（出栈，入栈，计算容积），但未尝不是一个好的尝试，这个方法还是有点小问题，过后会好好想清楚。看了网上提示完成了最终的方法，这个方法两次遍历数组，第一次遍历找每个元素右边最大的元素，第二次遍历寻找每个元素左边最大的元素，同时计算该阅读全文

posted @ 2014-05-14 04:37 neverlandly 阅读(594) 评论(0) 推荐(0) 编辑

Leetcode: Count and Say

摘要：The count-and-say sequence is the sequence of integers beginning as follows:1, 11, 21, 1211, 111221, ...1 is read off as "one 1" or 11.11 is read off ... 阅读全文

posted @ 2014-05-13 12:30 neverlandly 阅读(281) 评论(0) 推荐(0) 编辑

Leetcode: Valid Sudoku

摘要：Best Approach: '4' in row 7 is encoded as "(4)7". '4' in column 7 is encoded as "7(4)". '4' in the top-right block is encoded as "0(4)2". 然后在解Sudoku S 阅读全文

posted @ 2014-05-10 06:45 neverlandly 阅读(402) 评论(0) 推荐(0) 编辑

Leetcode: Search Insert Position

摘要：Given 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 or... 阅读全文

posted @ 2014-05-10 02:33 neverlandly 阅读(236) 评论(0) 推荐(0) 编辑

Leetcode: Swap Nodes in Pairs

摘要：1 Given a linked list, swap every two adjacent nodes and return its head.2 3 For example,4 Given 1->2->3->4, you should return the list as 2->1->4->3.... 阅读全文

posted @ 2014-05-10 01:32 neverlandly 阅读(253) 评论(0) 推荐(0) 编辑

Leetcode: Remove Nth Node From End of List

摘要：这道题要注意的Corner Case是：如果n比这个LinkedList的size大，那么就需要直接返回Head，如果相等，就把head删掉，返回head.next；基本做的方法呢，还是Runner Technique. 由于有可能head会被删掉，所以最好还是使用一个dummy node，dumm 阅读全文

posted @ 2014-05-09 04:55 neverlandly 阅读(367) 评论(0) 推荐(0) 编辑

Leetcode: Valid Parentheses

摘要：Given a string containing just the characters '(', ')', '{', '}', '[' and ']', determine if the input string is valid. The brackets must close in the 阅读全文

posted @ 2014-05-09 04:20 neverlandly 阅读(326) 评论(0) 推荐(0) 编辑

Leetcode: Merge Two Sorted Lists

摘要：方法二（推荐方法1）：新的Linkedlist不以任何现有List为依托，维护一个dummmy node和当前节点ListNode cur，把两个list的元素往里面插入作为cur.next，每次不new一个新的ListNode, 而是用已有的。相较于法一最后需要讨论两个list各自没有走完的情况阅读全文

posted @ 2014-05-09 03:38 neverlandly 阅读(815) 评论(0) 推荐(0) 编辑

Leetcode: Longest Common Prefix

摘要：这道题做的不够顺利，许多次通过，但是居然是卡在一个小问题上了，判断strs是否为空，我想当然地就写成了if(strs == null) return null; 报错 java中null表示还没new出对象，就是还没开辟空间；“”表示new出了对象，但是这个对象装的是空字符串。这里显然是要应对str 阅读全文

posted @ 2014-05-08 11:56 neverlandly 阅读(310) 评论(0) 推荐(0) 编辑

Leetcode: Roman to Integer

摘要：从右向左，preVal, curVal 1. curVal >= preVal: res+=curVal 2. curVal < preVal: res -= curVal 阅读全文

posted @ 2014-05-08 05:23 neverlandly 阅读(300) 评论(0) 推荐(0) 编辑

Leetcode: String to Integer

摘要：Implement atoi to convert a string to an integer.Hint: Carefully consider all possible input cases. If you want a challenge, please do not see below a... 阅读全文

posted @ 2014-05-08 03:27 neverlandly 阅读(379) 评论(0) 推荐(0) 编辑

Leetcode: Palindrome Numbers

摘要：Determine whether an integer is a palindrome. Do this without extra space.尝试用两头分别比较的方法，结果发现无法解决1000021这种问题 1 public class Solution { 2 public bool... 阅读全文

posted @ 2014-05-06 04:06 neverlandly 阅读(317) 评论(0) 推荐(0) 编辑

Leetcode: Reverse Integer

摘要：Reverse digits of an integer.Example1: x = 123, return 321Example2: x = -123, return -321一次通过，它的spoiler里面的提示有两个：1. 末尾为0的情况，这个考虑到了2.Did you notice that... 阅读全文

posted @ 2014-05-06 01:06 neverlandly 阅读(504) 评论(0) 推荐(0) 编辑

Leetcode: Two Sum

摘要：Given an array of integers, return indices of the two numbers such that they add up to a specific target. You may assume that each input would have ex 阅读全文

posted @ 2014-05-06 00:20 neverlandly 阅读(401) 评论(0) 推荐(0) 编辑

Leetcode: Path Sum

摘要：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.Fo... 阅读全文

posted @ 2014-05-05 12:02 neverlandly 阅读(283) 评论(0) 推荐(0) 编辑

Leetcode: Minimum Depth of Binary Tree

摘要：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 le... 阅读全文

posted @ 2014-05-04 22:32 neverlandly 阅读(295) 评论(0) 推荐(0) 编辑

Leetcode: Balanced Binary Tree

摘要：很锻炼DP/recursive思路的一道题，个人感觉DP/recursive算是比较难写的题目了。这道题解法的巧妙之处在于巧用-1，并且使用临时存储，节省了很多开支。这道题同时也在Career Cup上面出现过这道题我两次调试通过，第一次错是因为input{}, output false, exp 阅读全文

posted @ 2014-05-03 06:21 neverlandly 阅读(298) 评论(0) 推荐(0) 编辑

Leetcode: Maximum Depth of Binary Tree

摘要：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 le... 阅读全文

posted @ 2014-05-03 06:11 neverlandly 阅读(246) 评论(0) 推荐(0) 编辑

Leetcode: Same Tree

摘要：Given two binary trees, write a function to check if they are equal or not. Two binary trees are considered equal if they are structurally identical and the nodes have the same value. 1 public... 阅读全文

posted @ 2014-05-03 06:01 neverlandly 阅读(354) 评论(0) 推荐(1) 编辑

Leetcode: Remove Duplicates from Sorted List

摘要：Given a sorted linked list, delete all duplicates such that each element appear only once.For example,Given 1->1->2, return 1->2.Given 1->1->2->3->3, ... 阅读全文

posted @ 2014-05-03 05:56 neverlandly 阅读(273) 评论(0) 推荐(0) 编辑

Leetcode: Plus One

摘要：Given a non-negative number represented as an array of digits, plus one to the number.The digits are stored such that the most significant digit is at... 阅读全文

posted @ 2014-05-02 05:22 neverlandly 阅读(424) 评论(0) 推荐(0) 编辑

Leetcode: Length of Last Word

摘要：Given a string s consists of upper/lower-case alphabets and empty space characters ' ', return the length of last word in the string.If the last word ... 阅读全文

posted @ 2014-05-02 05:17 neverlandly 阅读(250) 评论(0) 推荐(0) 编辑

Leetcode: Remove Elements

摘要：Given 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 mat... 阅读全文

posted @ 2014-05-01 23:02 neverlandly 阅读(944) 评论(0) 推荐(0) 编辑

Leetcode: Remove Duplicates from Sorted Array

摘要：没有想通为什么这个简单的问题竟然不是那么简单，太小看它了，以下是别人的很不错的solution: Solution: 做法是维护两个指针，一个保留当前有效元素的长度，一个从前往后扫，然后跳过那些重复的元素。因为数组是有序的，所以重复元素一定相邻，不需要额外记录。时间复杂度是O(n)，空间复杂度O(1 阅读全文

posted @ 2014-05-01 12:24 neverlandly 阅读(339) 评论(0) 推荐(0) 编辑

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