DATA PROCESSING Gary Sham 15/1/2011

Data Processing  Data Processing ≠ Algorithm  Data Processing:  Get the input so that we can use it in our program.  Save the input by some method to make it easier to code.  How to prevent WA.  Our Goal: A general method to do Data Processing.  Practice makes perfect.  It is always useful in all programming problems. InputProcessingOutput

Data Types CategoryPascalC/C++ OrdinalInteger, Char, Boolean,...int, char, bool,... Floating PointReal, Double, Extended,...float, double,... ArrayArray[Range] of TypeType[Range] StringPChar, String, ANSIStringchar[Range], string Packed Data TypeRecordstruct OthersPtr, Set,...*Type, enum,... The table is by no means complete and the correspondence is not exact.

Floating Point  Floating Point Representation leads to Precision Error  1/3   0.15   Always try to use ordinal types instead, e.g. Integer.  More accurate; and  Operate faster generally.  Use most accurate floating type if possible.  Use some special operation to handle it.

Conversion to integer  How to handle floating point data?  Convert them to integers if possible  Integers are easy to manipulate  E.g. Given numbers to 2 decimal places   10  a := round(d*100);  a = (int)(d* )  Scanf is useful…  scanf(“%d.%d”, &a,&b);

Special operations  Output :  writeln((a+1e-10):0:2)  printf( “ %.2lf\n ”,a+1e-10);  Compare:  a==b abs(a-b) < 1e-8  a < b a < b – 1e-8  a <= b a < b + 1e-8  ……

String  Pascal:  1 byte storing length and 255 bytes storing array of characters.  Total size is 256 bytes by default.  C/C++  Null-terminating array of characters. Last byte (Null- character) denotes the end.

String processing  Pascal: normal assignment  s := ’abcde’;  t := s;  s[2] := ’9’;  C: by char *strcpy(char *dest, const char *src);  strcpy(s, "abcde");  strcpy(t, s);  s[1] = ’9’;  C++: normal assignment  s = "abcde";  t = s;  s[1] = ’9’;  Google it……

Hints  Do not use C function strlen in a loop……  e.g. for (int i=0;i<strlen(s);++i) {…}  C string is Null-terminating.  Also be careful on all string operations(strcpy, etc.)  int n = strlen(s); for (int i=0;i<n;++i) {…}

Packed Data Types  Record/struct  It increase the readability.  It is important when debugging.  Operator overloading(C++)

Mapping  Swapping the data may be slow  Records in Pascal  Strings/Struct in C/C++  Arrays  Use a pointer to represent the data.

 Hard-coding is important technique in tackling data processing problems  2067 – Tappy Game  Blocks MUST be hard-coded  What should we hard-code?  Number of blocks occupied for each column of each Tappy  4 rotations of each Tappy Hard-coding is much easier than writing codes for rotation! Hard-coding

 When you are doing some searching in a maze.  DFS/BFS?  Yes, but HOW?  if (x+1>0) && (x+1 0) && (y<n){…}  if (x-1>0) && (x-1 0) && (y<n){…}  if (x>0) && (x 0) && (y+1<n){…}  if (x>0) && (x 0) && (y-1<n){…}  ……………………

Hard-coding  How about 8 directions?!  int dy[8]={1,1,-1,-1,0,0,0,0};  int dx[8]={0,0,0,0,1,1,-1,-1};  We can use for loop now! :D  Shorter code

Exercise  1012 Allocating School Places  2042 Reversi  2030 Be Jewelled!  2080 Simple Calculator  2067 Tappy Game