c permutation of a number
- by Pkp
I am writing a program for magic box. As the only way around it is brute force, I wrote a program to compute permutations of a given array using bells algorithm. I wrote in the lines similar to http://programminggeeks.com/c-code-for-permutation/.
It does work for array of 3 and 4. It does not work for an arryay of 8 numbers (1,2,3,4,5,6,7,8). I see that the combination 1 2 3 4 5 6 7 8 gets repeated couple of times. Also there are other combinations that gets repeated. I see that certain combinations don't get displayed even. So could someone tell me what is wrong in the program below.
Code:
include<stdio.h>
int len,numperm=1,count=0;
display(int a[]){
int i;
for(i=0;i<len;i++)
printf("%d ",a[i]);
printf("\n");
count++;
}
swap(int *a,int *b){
int temp;
temp=*a;
*a=*b;
*b=temp;
}
no_of_perm(){
int x;
for(x=1;x<=len;x++)
numperm=numperm*x;
}
perm(int a[]){
int x,y;
while(count < numperm){
for(x=0;x<len-1;x++){
swap(&a[x],&a[x+1]);
display(a);
}
swap(&a[0],&a[1]);
display(a);
for(y=len-1;y>0;y--){
swap(&a[y],&a[y-1]);
display(a);
}
swap(&a[len-1],&a[len-2]);
display(a);
}
}
main(int argc, char *argv[]){
if(argc<2){
printf("Error\n");
exit(0);
}
int i,*a=malloc(sizeof(int)*atoi(argv[1]));
len=atoi(argv[1]);
for(i=0;i<len;i++)
a[i]=i+1;
no_of_perm();
perm(a);
}
