2014 年 6月随笔档案 - neverlandly

Leetcode: Permutations

摘要：Given a collection of numbers, return all possible permutations.For example,[1,2,3] have the following permutations:[1,2,3], [1,3,2], [2,1,3], [2,3,1]... 阅读全文

posted @ 2014-06-27 13:14 neverlandly 阅读(448) 评论(0) 推荐(0) 编辑

Leetcode: First Missing Positive

摘要：Given 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 sho... 阅读全文

posted @ 2014-06-27 07:55 neverlandly 阅读(271) 评论(0) 推荐(0) 编辑

Summary: Binary Search

摘要：Iterative ways: 1 int binarySearch (int[] a, int x) { 2 int low = 0; 3 int high = a.length - 1; 4 int mid; 5 6 while (low x) {12 ... 阅读全文

posted @ 2014-06-27 06:43 neverlandly 阅读(196) 评论(0) 推荐(0) 编辑

Leetcode: Find First and Last Position of Element in Sorted Array

摘要：Analysis: 这道题是二分查找Search Insert Position的变体，思路并不复杂，就是先用二分查找找到其中一个target，然后再往左右找到target的边缘。找边缘的方法跟二分查找仍然是一样的，只是相等的情况依然要往左找（找左边缘）或往右找（找右边缘）。这样下来总共进行了三次二阅读全文

posted @ 2014-06-27 06:26 neverlandly 阅读(336) 评论(0) 推荐(0) 编辑

Leetcode: Unique Binary Search Trees

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

posted @ 2014-06-26 12:26 neverlandly 阅读(227) 评论(0) 推荐(0) 编辑

Leetcode: Group Anagrams

摘要：if want lexicographic order，然后要用Collections.sort() 来保证字典序 for (List<String> each : map.values()) { Collections.sort(each); res.add(new ArrayList<Strin 阅读全文

posted @ 2014-06-26 08:10 neverlandly 阅读(387) 评论(0) 推荐(0) 编辑

Leetcode: Reverse Linked List II

摘要：Reverse a linked list from position m to n. Do it in-place and in one-pass.For example:Given 1->2->3->4->5->NULL, m = 2 and n = 4,return 1->4->3->2->5... 阅读全文

posted @ 2014-06-25 12:35 neverlandly 阅读(252) 评论(0) 推荐(0) 编辑

Leetcode: Longest Valid Parentheses

摘要：Given a string containing just the characters '(' and ')', find the length of the longest valid (well-formed) parentheses substring.For "(()", the lon... 阅读全文

posted @ 2014-06-25 06:18 neverlandly 阅读(334) 评论(0) 推荐(0) 编辑

Leetcode: Partition List

摘要：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 o... 阅读全文

posted @ 2014-06-24 23:11 neverlandly 阅读(494) 评论(0) 推荐(0) 编辑

Leetcode: Rotate List

摘要：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->... 阅读全文

posted @ 2014-06-23 23:28 neverlandly 阅读(251) 评论(0) 推荐(0) 编辑

Leetcode: Divide Two Integers

摘要：Best method(跟discuss vote最高相似)：只有一种情况整数除以整数会overflow，那就是Integer.MIN_VALUE除以-1，这种情况特殊分析。之所以要用long a, b代替dividend和divisor是因为：比如Integer.MAX_VALUE除以1，第21 阅读全文

posted @ 2014-06-21 06:31 neverlandly 阅读(352) 评论(0) 推荐(0) 编辑

Leetcode: Linked List Cycle II

摘要：Given a linked list, return the node where the cycle begins. If there is no cycle, return null.Follow up:Can you solve it without using extra space?一次... 阅读全文

posted @ 2014-06-20 08:04 neverlandly 阅读(235) 评论(0) 推荐(0) 编辑

Leetcode: Single Number II

摘要：Given an array of integers, every element appears three times except for one. Find that single one.Note:Your algorithm should have a linear runtime co... 阅读全文

posted @ 2014-06-20 07:49 neverlandly 阅读(262) 评论(0) 推荐(0) 编辑

Leetcode: Linked List Cycle

摘要：Given a linked list, determine if it has a cycle in it.Follow up:Can you solve it without using extra space?Analysis: typical Runner Technique. 一次过 1 ... 阅读全文

posted @ 2014-06-20 07:14 neverlandly 阅读(236) 评论(0) 推荐(0) 编辑

Leetcode: Binary Tree Preorder Traversal

摘要：Analysis: 第一反应肯定是recursion(递归), 非常直接，但是题目要求不能用递归。如果要使用迭代的方法来写preorder traversal，最大的问题是要如何确定遍历节点的顺序，因为树的pre-order traversal其实很类似图的DFS，DFS可以用Stack来写，所以这阅读全文

posted @ 2014-06-19 12:54 neverlandly 阅读(434) 评论(0) 推荐(0) 编辑

Leetcode: Single Number

摘要：Analysis: 需求里面要求O(N)时间以及无额外空间，这就排除了使用boolean array, hashmap这些个方法，只能在原数组上进行查找。O(N)基本上就相当于遍历数组. 最好的方法：第二遍做法： 17行 & 运算符优先等级低于 == 所以一定要打括号一样的思路另一个做法：另外阅读全文

posted @ 2014-06-19 06:37 neverlandly 阅读(309) 评论(0) 推荐(0) 编辑

Leetcode: Combination Sum

摘要：典型的recursion方法，找符合要求的path，存入result的ArrayList中。所以方法还是建立一个ArrayList<ArrayList<Integer>> result, 建立一个ArrayList<Integer> path，用recursion当找到符合条件的path时，存入re 阅读全文

posted @ 2014-06-19 05:57 neverlandly 阅读(373) 评论(0) 推荐(0) 编辑

Leetcode: Rotate Image

摘要：抠细节的题，题目思想如下：to implement the rotation in layers, if size is n, so there will be (int)(n / 2) layers that should be rotated. 需要注意的是：在下面这段code里面，需要注意的是阅读全文

posted @ 2014-06-18 12:05 neverlandly 阅读(432) 评论(0) 推荐(0) 编辑

Leetcode: Longest Palindromic Substring && Summary: Palindrome

摘要：Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000. Example 1: Example 2: Analysis: 想到阅读全文

posted @ 2014-06-17 12:07 neverlandly 阅读(587) 评论(0) 推荐(0) 编辑

Leetcode: Reverse Nodes in k-Group

摘要：Given a linked list, reverse the nodes of a linked list k at a time and return its modified list.If the number of nodes is not a multiple of k then le... 阅读全文

posted @ 2014-06-17 04:58 neverlandly 阅读(491) 评论(0) 推荐(0) 编辑

Leetcode: Substring with Concatenation of All Words

摘要：You are given a string, S, and a list of words, L, that are all of the same length. Find all starting indices of substring(s) in S that is a concatena... 阅读全文

posted @ 2014-06-14 00:40 neverlandly 阅读(334) 评论(0) 推荐(0) 编辑

Leetcode: Merge k Sorted List

摘要：参看别人的思路，类似MergeSort的思路，思路是先分成两个子任务，然后递归求子任务，最后回溯回来。这个题目也是这样，先把k个list分成两半，然后继续划分，直到剩下两个list就合并起来，合并时会用到Merge Two Sorted Lists这道题。 MergeSort的方法：我们来分析一下上阅读全文

posted @ 2014-06-12 12:53 neverlandly 阅读(441) 评论(0) 推荐(0) 编辑

Summary: Java中函数参数的传递

摘要：函数调用参数传递类型（java）的用法介绍.java方法中传值和传引用的问题是个基本问题，但是也有很多人一时弄不清。（一）基本数据类型：传值，方法不会改变实参的值。 1 public class TestFun { 2 3 public static void testInt(int ... 阅读全文

posted @ 2014-06-12 05:54 neverlandly 阅读(3029) 评论(0) 推荐(0) 编辑

Leetcode: Generate Parentheses

摘要：又是把所有满足条件的结果存到一个ArrayList里面，之前也有类似的如Letter combination of a Phone Number这道题。这种类型的题其实形成了一个套路，套路就是，recursion参数包括最终结果的集合（ArrayList），input（String），递归层次le 阅读全文

posted @ 2014-06-12 01:55 neverlandly 阅读(418) 评论(0) 推荐(0) 编辑

Leetcode: Longest Substring Without Repeating Characters

摘要：Use HashSet Use HashMap 阅读全文

posted @ 2014-06-11 03:24 neverlandly 阅读(353) 评论(0) 推荐(0) 编辑

Leetcode: ZigZag Conversion

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 ... 阅读全文

posted @ 2014-06-11 03:12 neverlandly 阅读(289) 评论(0) 推荐(0) 编辑

Leetcode: Letter Combinations of a Phone Number

摘要：像这种DFS的题目，常见的写法无外乎两种，使用recursion, 或者用Stack。本文采用了Recursion的方式。做完后积累的经验有：像这种在一个ArrayList里面罗列可能的path的题目，recursion的参数一般包括：包含最终结果的集合（ArrayList），input（Strin 阅读全文

posted @ 2014-06-11 02:24 neverlandly 阅读(665) 评论(0) 推荐(0) 编辑

Summary: Depth-first Search(DFS)

摘要：There are generally two methods to write DFS algorithm, one is using recursion, another one is using stack. （reference from Wiki Pedia）Pseudocode for ... 阅读全文

posted @ 2014-06-11 02:09 neverlandly 阅读(611) 评论(0) 推荐(0) 编辑

Leetcode: Integer to Roman

摘要：Given an integer, convert it to a roman numeral.Input is guaranteed to be within the range from 1 to 3999.一次过 1 public class Solution { 2 public S... 阅读全文

posted @ 2014-06-10 13:07 neverlandly 阅读(332) 评论(0) 推荐(0) 编辑

Leetcode: Container With Most Water

摘要：这道题我考虑过类似Trapping most water的做法，不大一样。那道题寻找左右最大元素，我可以确定那就是最优解，但是在这里，即使寻到了左右最大元素，我也不敢确定那是最优解。然后我有考虑了DP全局最优&局部最优的做法，发现局部最优的递推式很难写。所以没有法了，网上看到说这道题用夹逼方法 T 阅读全文

posted @ 2014-06-10 13:06 neverlandly 阅读(287) 评论(0) 推荐(0) 编辑

Leetcode: Add Two Numbers

摘要：You are given two linked lists representing two non-negative numbers. The digits are stored in reverse order and each of their nodes contain a single ... 阅读全文

posted @ 2014-06-06 23:56 neverlandly 阅读(247) 评论(0) 推荐(0) 编辑

Leetcode: Word Ladder II

摘要：Given two words (start and end), and a dictionary, find all shortest transformation sequence(s) from start to end, such that:Only one letter can be ch... 阅读全文

posted @ 2014-06-05 21:07 neverlandly 阅读(386) 评论(0) 推荐(0) 编辑

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