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.

Input Processing Output

Data Types

Category Pascal C/C++

Ordinal Integer, Char, Boolean, . . .

int, char, bool, . . .

Floating Point Real, Double, Extended, . . .

float, double, . . .

Array Array[Range] of Type Type[Range]

String PChar, String, ANSIString

char[Range], string

Packed Data Type Record struct

Others Ptr, Set, . . . *Type, enum, . . .The table is by no means complete and the correspondence is not exact.www.google.com

Floating Point

Floating Point Representation leads to Precision Error 1/3 0.3333333 0.15 0.149999

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

123.45 12345 0.10 10

a := round(d*100); a = (int)(d*100 + 0.5)

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

Hard-coding

When you are doing some searching in a maze.

DFS/BFS? Yes, but HOW?

if (x+1>0) && (x+1<n) && (y>0) && (y<n){…} if (x-1>0) && (x-1<n) && (y>0) && (y<n){…} if (x>0) && (x<n) && (y+1>0) && (y+1<n){…} if (x>0) && (x<n) && (y-1>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