ACM/ICPC SELF TRAINING

##SOME NEW FACTS TO ME (SEP 2013)##

• Java

  • StreamTokenizer and PrintWriter is faster than Scanner and System.out
  • Reform of Token from StreamTokenizer is necessary: (int)input.nextToken()
  • Use multiple Scanner in one program will cause problem (Runtime Error).
  • Java cannot manipulate each elements in the string (read only). So, if you don't like subString() method, you can easily use toCharArray() method to do such operation.
  • Generally, Java is slower than C++ (especially for manipulating character and IO)
  • If you want to duplicate an array in a short time, use clone() method
  • Java's split() method is a masterpiece, can make code shorter.
  • Arrays.sort() has range [1,n). So if you are sorting an Array with 1~n, you should call Arrays.sort(a,1,n+1).
  • BigInteger and BigDecimal is good to use, but very very slow.
  • replace() method in String is a little bitch, so be careful.

• C++

  • This code will redirect standard IO stream to file IO stream: freopen("input.in","r",stdin); freopen("output.out","w",stdout); Use such code, you can read data from file directly with cin and cout.
  • Although removing character in string is a bit difficult, however, if you can change the character you want to remove to an unique character, it will looks like being removed.
  • Remember to use EOF when there is no end. (can't be seen in keyboard input, but can use file to demonstrate.

• UVa

  • When you use Java, change your main class as "class Main{}" before submission.
  • Make sure print new line at the end of the file.
  • Some critical tests are needed.
  • If you have mixed input (have both number and string in input), try to read all of them as string and convert string to number.

• URAL

  • Sometimes, the relationship between numbers are much more effective than use searching algorithm.
  • If you have n integers and want to determine the median, there is an O(N) (not exactly O(N)) solution. By using priority queue, load first n/2+1 numbers, and then load another n/2, meanwhile, keep popping the one with highest priority.
  • Sometimes, precision of numbers is very very important. You may want to rescale the number or add an very small number (e.x.: 0.0000001) to keep the precision.

###Contacts### Hu Yuhuang (duguyue100)

Email: [email protected]

Address: No.42, North, Flatland.