北京大學ACM比賽題目
Write a program to read four lines of upper case (i.e., all CAPITAL Letters) text input (no more than 72 characters per line) from the input file and print a vertical histogram that shows how many times each letter (but not blanks, digits, or punctuation) appears in the all-upper-case input. Format your output exactly as shown.
This scheme is initiated by Ziv and Lempel [1]. A slightly modified version is described by Storer and Szymanski [2]. An implementation using a binary tree is proposed by Bell [3]. The algorithm is quite simple: Keep a ring buffer, which initially contains "space" characters only. Read several Letters from the file to the buffer. Then search the buffer for the longest string that matches the Letters just read, and send its length and position in the buffer.
The government of a small but important country has decided that the alphabet needs to be streamlined and reordered. Uppercase Letters will be eliminated. They will issue a royal decree in the form of a String of B and A characters. The first character in the decree specifies whether a must come ( B )Before b in the new alphabet or ( A )After b . The second character determines the relative placement of b and c , etc. So, for example, "BAA" means that a must come Before b , b must come After c , and c must come After d .
Any Letters beyond these requirements are to be excluded, so if the decree specifies k comparisons then the new alphabet will contain the first k+1 lowercase Letters of the current alphabet.
Create a class Alphabet that contains the method choices that takes the decree as input and returns the number of possible new alphabets that conform to the decree. If more than 1,000,000,000 are possible, return -1.
Definition
四套Latex模版，分別是：
A good model for writing Curriculum Vitae；
An excellent package to design slides using LaTeX；
A strong package to make floating figure and table style；
For writing formal Letters。
TFIND
searches for one or more strings (boolean AND) in a text file.
TFIND reports all lines where the string(s) were found (or NOT found
by option).
The search can be limited to a field in a fixed field (i.e. column
oriented) list.
An extended search mode is available, where only Letters and digits
are relevant.
Other options:
case sensitive search,
alternative errorlevel with number of hits,
header line with file name, LFN, custom prefix
RTOS ThreadX
Real-Time Embedded
Multithreading:
Using ThreadX and ARM
Designations used by companies to distinguish their products are often claimed as trademarks. In all instances
where CMP is aware of a trademark claim, the product name appears in initial capital Letters, in all capital
Letters, or in accordance with the vendor鈥檚 capitalization preference. Readers should contact the appropriate
companies for more complete information on trademarks and trademark registrations. All trademarks and
registered trademarks in this book are the property of their respective holders.
Playfair Cipher
1.not even the large number of keys in a monoalphabetic cipher provides security
2.one approach to improving security was to encrypt multiple Letters
3.the Playfair Cipher is an example
4.invented by Charles Wheatstone in 1854,but named after his friend Baron Playfair
Playfair Key Matrix
1.a 5X5 matrix of Letters based on a keyword
2.fill in Letters of keyword (sans duplicates)
3.fill rest of matrix with other Letters
Encrypting and Decrypting
-plaintext is encrypted two Letters at a time
1. if a pair is a repeated letter, insert filler like X’
2. if both Letters fall in the same row, replace each with letter to right (wrapping back to start from end)
3. if both Letters fall in the same column, replace each with the letter below it (again wrapping to top from
bottom)
4. otherwise each letter is replaced by the letter in the same row and in the column of the other letter of the pair
