optimize random numbers b/w 1 to n w/o repetition

[powinda]

Hi,
I am writing this to be used as generating an initial random permutation from 1 to n out of which a graph will be constructed on which the algorithm for the quadratic assignment problem will be used. Since the whole goal is time effeciency and better optimized code, how can i make this code more optimized and a little less lines of code

#include <stdio.h>
#include <stdlib.h>
#include <iostream.h>
#include <time.h>


int main() {

	int test = 0,a = 0, i = 0,n = 0, k = 0, *perm;

	printf("Enter value of n: ");
	scanf("%d",&n);
	printf("size of the permutation array is [%d]\n",n);
	
	perm = new int[n];
	if(perm == NULL)
		printf("Unable to assign memory to permutation array of size [%d]\n",n);
	for (k = 0;k < n;k++)
		perm[k] = 0;

	srand(time(0));
	while(i != n) {
		a = 1 + (rand() % n);
		if( a <= n && a >= 1){			
			for (k = 0;k < n;k++){
				if( a == perm[k])
					test = 1;
			} 
			if (test != 1)
			{
				perm[i] = a;
				i++;
			}
			else
				test =0;
			
		}
	}
	for (k=0;k < n;k++)
		printf("[%d]",perm[k]);
	printf("\n");
	
	delete [] perm;
	return 0;
}

[lmov]

Hello,

You can make an array of elements 1...n and then shuffle them to get a random premutation:

#include <vector>
#include <algorithm>
#include <iostream>

int main()
{
    const int N = 20;
    std::vector<int> vec(N);
    for(int i(1); i <= N; ++i) vec[i - 1] = i;
    std::random_shuffle(vec.begin(), vec.end());
    std::copy(vec.begin(), vec.end(),
        std::ostream_iterator<int>(std::cout, " "));
}

[powinda]

This works but it will always generate the same random permutation of numbers over the length of the vector. Do you know that random_shuffle call is being seeded to time or not. I think it is not. Is their any other function call like this that is seeded to time. I will try to look into the header file "algorithm.h" but if anybody else knows will appreciate

[lmov]

random_shuffle uses rand by default so you can seed it with srand.