Coin Change 2 (LeetCode518)

Solution
You are given coins of different denominations and a total amount of money. Write a function to compute the number of combinations that make up that amount. You may assume that you have infinite number of each kind of coin.

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Example 1:

Input: amount = 5, coins = [1, 2, 5]
Output: 4
Explanation: there are four ways to make up the amount:
5=5
5=2+2+1
5=2+1+1+1
5=1+1+1+1+1
Example 2:

Input: amount = 3, coins = [2]
Output: 0
Explanation: the amount of 3 cannot be made up just with coins of 2.
Example 3:

Input: amount = 10, coins = [10] 
Output: 1

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JavaWeb学习笔记之Servlet，HTTP

Queue Reconstruction by Height（LeetCode 406）

Suppose you have a random list of people standing in a queue. Each person is described by a pair of integers (h, k), where h is the height of the person and k is the number of people in front of this person who have a height greater than or equal to h. Write an algorithm to reconstruct the queue.

Note:
The number of people is less than 1,100.

Example

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Input:
[[7,0], [4,4], [7,1], [5,0], [6,1], [5,2]]

Output:
[[5,0], [7,0], [5,2], [6,1], [4,4], [7,1]]

Random Pick with Weight

Solution

Given an array w of positive integers, where w[i] describes the weight of index i, write a function pickIndex which randomly picks an index in proportion to its weight.

Note:

1. 1 <= w.length <= 10000
2. 1 <= w[i] <= 10^5
3. pickIndex will be called at most 10000 times.

Example 1:

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Input: 
["Solution","pickIndex"]
[[[1]],[]]
Output: [null,0]

Example 2:

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Input: 
["Solution","pickIndex","pickIndex","pickIndex","pickIndex","pickIndex"]
[[[1,3]],[],[],[],[],[]]
Output: [null,0,1,1,1,0]

Explanation of Input Syntax:

The input is two lists: the subroutines called and their arguments. Solution‘s constructor has one argument, the array w. pickIndex has no arguments. Arguments are always wrapped with a list, even if there aren’t any.

Reverse String

1. Write a function that reverses a string. The input string is given as an array of characters char[].

   Do not allocate extra space for another array, you must do this by modifying the input array in-place with O(1) extra memory.

   You may assume all the characters consist of printable ascii characters.

Example 1:

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Input: ["h","e","l","l","o"]
Output: ["o","l","l","e","h"]

Example 2:

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Input: ["H","a","n","n","a","h"]
Output: ["h","a","n","n","a","H"]

本文概述

JavaWeb学习笔记之XML

XML

1. 概念：Extensible Markup Language 可扩展标记语言

   • 可扩展：标签都是自定义的。
   • 功能
     • 存储数据
       1. 配置文件
       2. 在网络中传输
   • xml与html的区别
     1. xml标签都是自定义的，html标签是预定义。
     2. xml的语法严格，html语法松散
     3. xml是存储数据的，html是展示数据
   • w3c:万维网联盟

本文概述

JavaWeb学习笔记之JDBC

JDBC

概念

• Java Database Connectivity Java数据库连接，Java语言操作数据库。
• 定义一套操作所有关系型数据库的接口

本文概述

JavaWeb学习笔记之Bootstrap

Bootstrap：

1. 框架:一个半成品软件，开发人员可以在框架基础上，在进行开发，简化编码。

2. 好处：

   1. 定义了很多的css样式和js插件。我们开发人员直接可以使用这些样式和插件得到丰富的页面效果。
   2. 响应式布局。
      • 同一套页面可以兼容不同分辨率的设备。

3. 快速入门

   1. 下载Bootstrap
   2. 在项目中将这三个文件夹复制
   3. 创建html页面，引入必要的资源文件

Two City Scheduling

Solution

There are 2N people a company is planning to interview. The cost of flying the i-th person to city A is costs[i][0], and the cost of flying the i-th person to city B is costs[i][1].

Return the minimum cost to fly every person to a city such that exactly N people arrive in each city.

Example 1:

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Input: [[10,20],[30,200],[400,50],[30,20]]
Output: 110
Explanation: 
The first person goes to city A for a cost of 10.
The second person goes to city A for a cost of 30.
The third person goes to city B for a cost of 50.
The fourth person goes to city B for a cost of 20.

The total minimum cost is 10 + 30 + 50 + 20 = 110 to have half the people interviewing in each city.

Note:

1. 1 <= costs.length <= 100
2. It is guaranteed that costs.length is even.
3. 1 <= costs[i][0], costs[i][1] <= 1000

Delete Node in a Linked List

Write a function to delete a node (except the tail) in a singly linked list, given only access to that node.

Given linked list – head = [4,5,1,9], which looks like following:

Example 1:

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Input: head = [4,5,1,9], node = 5
Output: [4,1,9]
Explanation: You are given the second node with value 5, the linked list should become 4 -> 1 -> 9 after calling your function.

Example 2:

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Input: head = [4,5,1,9], node = 1
Output: [4,5,9]
Explanation: You are given the third node with value 1, the linked list should become 4 -> 5 -> 9 after calling your function.

Note:

• The linked list will have at least two elements.
• All of the nodes’ values will be unique.
• The given node will not be the tail and it will always be a valid node of the linked list.
• Do not return anything from your function.