Usenet 1994 January/usenetsourcesnewsgroupsinfomagicjanuary1994.iso/sources/unix/volume17/contest-prog/part03/prob18.c

C/C++ Source or Header | 1989-02-06 | 4.9 KB | 186 lines

/*
Problem 18:Expanding square codes

   One method of encoding messages is known as the "expanding square
code."  This method encodes messages by placing the characters of the
message to be encoded in an odd order(1,3,5,7,9) square matrix row by
row, and then retrieves them (decoding) in a clockwise expanding
square spiral from the center of the matrix.  If the message is not
exactly the right length to fill the matrix, the rest of the matrix
is filled with asterisk characters (*).

   For example, the two square matrices below show the order in which
the characters are placed in a matrix(order 5), and the order in which
they are to be retrieved.  Notice that the order of retrieval begins
at the center, then proceeds to the right, and then spirals
clockwise.

      order in                       order out

      1   2   3   4   5               21  22  23  24  25
      6   7   8   9  10               20   7   8   9  10
     11  12  13  14  15               19   6   1   2  11
     16  17  18  19  20               18   5   4   3  12
     21  22  23  24  25               17  16  15  14  13

 Examples:

   encode:
     message in:  "This is a test message!"

     message out: "stssees a  a**!egmtiThis "

   decode:
     message in:  "anreh is io *.enotshAnd t"

     message out: "And this is another one."

   Your program should be able to encode and to decode messages by
this method.  The input will consist of pairs of lines; the first
line in each pair will contain either the word   encode   or the word
decode   in lower case characters.  The second line in each pair will
consist of a message to be either encoded or decoded by the above
method, containing a maximum of 80 characters.  There will be no
quotation marks (") surrounding the messages, and you should not
output your messages with "'s.

   From the length of the message, you should determine the minimum
odd order required for the matrix, and perform the specified operation.
The output for each operation will consist of one blank line, the
given message, and the resultant message.  Each message should be
on a separate line. A decoded message may not contain the asterisk
characters used to fill the matrix in the encoding process.  You
may assume that no actual message contains an asterisk.

   Your program should continue reading input lines and performing
operations until something other than the words   encode  or
decode  is encountered.

Here is an actual run; the input file consisted of exactly four lines.
The output file consists of exactly six lines; lines 1 and 4 are
blank lines.
This was the input file (the next four lines):
encode
now is the time for all
decode
imroft thee **lla  snow i
Here was the output file (the next six lines, NOTICE the blank lines!):

now is the time for all
imroft thee **lla  snow i

imroft thee **lla  snow i
now is the time for all
*/
#include <stdio.h>
#include <kindex.c>
#define newline '\n'
#define null '\0'
int E[]={0,1};
int S[]={1,0};
int W[]={0,-1};
int N[]={-1,0};
int *dir;
int x,y;
int size;
#define SZ 55
int a[SZ+3][SZ+3];

main(){
    int len,d,n,i,k,j,jj;
    char line[256];

    while( gets(line)==line){
    if(kindex(line,"encode")==0)goto encode;
    if(kindex(line,"decode")==0)goto decode;
    exit(0);
    encode:
    putchar(newline);
    gets(line);
    puts(line);
    for(i=0;i<=90;i++)if(line[i]==newline ||line[i]==null)break;
    line[i]=null;
    len=i;
    for(size=1;;size++,size++)if(size*size>=len)break;
    for(i=len;i<size*size;i++)line[i]='*';line[i]=null;
for(i=1;i<=SZ;i++)for(k=1;k<=SZ;k++){a[i][k]= 0;}
j=0;
for(i=1;i<=size;i++)for(k=1;k<=size;k++){a[i][k]=line[j++];}
/*
for(i=1;i<=size;i++)
{
    for(k=1;k<=size;k++){
            printf("%c",a[i][k]);
    }
    putchar(newline);}
    */
    x=y=(size+1)/2;
    n=size*size;
    dir=E;
    printf("%c",a[x][y]);
    for(k=1;k<=size;k++){
        for(j=1;j<=k;j++){
        d=godir();if(d>0)printf("%c",d); if(d<0)goto out;
        }
        nextdir();
        for(j=1;j<=k;j++){
        d=godir();if(d>0)printf("%c",d); if(d<0)goto out;
        }
        nextdir();
    }
    out:putchar(newline);
    goto getnextline;

    decode:
    /*for(i=0;i<=SZ;i++)for(j=0;j<=SZ;j++)a[i][j]=1;*/
    putchar(newline);
    gets(line);
    for(i=0;i<=90;i++)if(line[i]==newline ||line[i]==null)break;
    line[i]=null;
    puts(line);
    len=i;
    for(size=1;;size++,size++)if(size*size>=len)break;
    for(i=len;i<size*size;i++)line[i]=' ';line[i]=null;
    x=y=(size+1)/2;
    n=size*size;
    dir=E;
    jj=0;
    a[x][y]=line[jj++];
    for(k=1;k<=size;k++){
        for(j=1;j<=k;j++){
        d=godir();a[x][y]=line[jj++]; if(jj>n)goto out1;
/*        printf("x,y= %d %d\n",x,y);*/
        }
        nextdir();
        for(j=1;j<=k;j++){
        d=godir();a[x][y]=line[jj++]; if(jj>n)goto out1;
/*        printf("x,y= %d %d\n",x,y);*/
        }
        nextdir();
    }
    out1:
    jj=0;
    for(i=1;i<=size;i++)for(j=1;j<=size;j++)line[jj++]=a[i][j];
    for(i=0;i<100;i++)if(line[i]=='*')line[i]=null;
    puts(line);
getnextline: ;
}
}
godir()
{
    x= x+ dir[0];
    y= y+ dir[1];
    if(y<1 || y>size)return -1;
    if(x<1 || x>size)return -1;
    return a[x][y];

}
nextdir()
{
    if(dir==E){dir=S;return;}
    if(dir==S){dir=W;return;}
    if(dir==W){dir=N;return;}
    if(dir==N){dir=E;return;}

}