# RC4 加密算法

RC4 是一种对称加密算法，使用的密钥为单钥。RC4 是用字节流的方式依次加密明文中的每一个字节，解密的时候也是依次对密文中的每一个字节进行解密。用密钥生成与明文一样长短的密码流对明文进行加密，加解密使用相同的密钥。

# DES 数据加密标准

DES 是由美国 IBM 公司基于 Horst Feistel 提出的理论研制出来的加密算法，于 1977 年 1 月 15 日由美国国家标准局颁布为数据加密标准（Data Encryption Standard）。

# DH 密钥交换算法

Diffie-Hellman-Merkle(DH) 算法是最早的公钥交换算法之一。DH 算法在公共网络中建立了一个可靠的通信通道。

# POJ3684 Physics Experiment

## Description

Simon is doing a physics experiment with N identical balls with the same radius of R centimeters. Before the experiment, all N balls are fastened within a vertical tube one by one and the lowest point of the lowest ball is H meters above the ground. At beginning of the experiment, (at second 0), the first ball is released and falls down due to the gravity. After that, the balls are released one by one in every second until all balls have been released. When a ball hits the ground, it will bounce back with the same speed as it hits the ground. When two balls hit each other, they with exchange their velocities (both speed and direction).

# POJ3279 Fliptile

## Description

Farmer John knows that an intellectually satisfied cow is a happy cow who will give more milk. He has arranged a brainy activity for cows in which they manipulate an M × N grid (1 ≤ M ≤ 15; 1 ≤ N ≤ 15) of square tiles, each of which is colored black on one side and white on the other side.

# POJ3276 Face The Right Way

## Description

Farmer John has arranged his N (1 ≤ N ≤ 5,000) cows in a row and many of them are facing forward, like good cows. Some of them are facing backward, though, and he needs them all to face forward to make his life perfect.

# POJ2010 Moo University - Financial Aid

## Description

Bessie noted that although humans have many universities they can attend, cows have none. To remedy this problem, she and her fellow cows formed a new university called The University of Wisconsin-Farmside,"Moo U" for short.

# priority_queue 的使用(C++)

• 插入一个数值
• 去除最小（大）的数值（获得数值，并且删除）