Heya. As i write this i admit i am blushing rather violently. This shouldn''t be a hard thing to but i just get my head around it... Basically i am trying to do the following. Get a program to generate a strings of 5 random numbers, using the numbers 1-5. OK so far! But the problems begin with the filtering rules: (i) must only use each digit once (no repetitions within string) (ii) the next string can''t begin with the same first digit as the last string (iii) (the hard one i think) the next string can''t have any 3 numbers in the same order as they were in the preceeding string. so this would be invalid: 1,5,4,3,2 5,4,3,2,1 (cos of the 4,3,2 thingy). I would be embaressingly grateful for any help you might care to furnish me with! (C,C++ or any dialect of BASIC) R.

First I would put the numbers to arrays. When done processing make the strings. Unless you need to make many strings it wouldn''t make any difference if your algorithms are n^2. So you can take the easiest sollution, namly check everything for everything. I am sure you know how, if you think.

Yeah...umm. That sort of how i''ve tried to implement it. But the checking everything for everything part is still a pain to do. I was sort of hoping that buried deep within C++ there was a some sort of funky string-handling fuction which would do it...

Well, My first incling would be use an array and store the previously generated string. Then I would generate a new string and then compare each element. If you find anything in order, just do a swap of the first one.

string 1
1,3,5,2,6

string 2a
3,1,5,2,6 -> after comparion

3,1,2,5,6

Problem solved!

Try that out

Kevin =)

Probably not the best way to do it. but it appears to work right and is pretty simple.

  #include <stdio.h>#include <stdlib.h>#include <string.h>int check3(char *a, char *b) {char dat[6]; int i;for (i=0; i<3; i++) {strcpy(dat, a);dat[i+3]=0;if (strstr(b, dat+i)) return 1; }return 0;}char last[6];void randspecial(char *n) {	int taken[5]={0,0,0,0,0};	int i;    for (i=0; i<5; i++) {	int r = rand()%5;	while(taken[r]) {r++; r=r%5;}	n<i>=r+''1''; taken[r]=1;	}    if (check3(n, last)) {randspecial(n);}	strcpy(last, n);}void main() {		while (getch()!=27) {          char dat[6];	  dat[5]=0;	  randspecial(dat);	  printf("\n%s", dat);	}}  

You will need lots of loops. In the common loop you will need to test the new array with all the others, one by one, unfortunately.

I forgot to tell you, don´t test 3 against 3 all the time. Optimize it, use 1 by 1. If there is some equal numbers, test the next int of the matching arrays. Only if this happens you need to test the third. This will get it almost 3 times faster.