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# Answer to Question #62422 in C for LEE JIA WEI

Question #62422
Generate a 2D array of size 20 x 20 comprising 0 or 1 using a RAND generator. Ensure the following: 1- Seed your generator with a different seed (time of the day for instance) each time you re-execute the code. 2- Your 2D array must be symmetric, i.e., corresponds to a valid adjacency matrix. That is, if there is an edge between (i,j) then this means there is an edge between nodes (j,i). So think carefully in generating your 2D matrix.
#include <stdio.h>
#include <stdlib.h>
#include <time.h>

int *random_matrix(const size_t v, const size_t e, const unsigned int seed);
int *random_sequence(const size_t n, const size_t k, const unsigned int seed);

int main(void)
{
int *graph;
graph = random_matrix(20, 11, time(0));

/* a chance to do something */

free(graph);

return 0;
}

int *random_matrix(const size_t v, const size_t e, const unsigned int seed)
{
int *matr;
size_t i, j;
int *seq;

if (e > (v - 1) * v / 2) exit(1);

matr = (int *) calloc(v * v, sizeof(int));
seq = random_sequence((v - 1) * v / 2, e, seed);
for (j = 0; j < v; j++)
for (i = 0; i < j; i++) {
/* or simply set matr[i + j * v] = seq[count++] */
matr[i + j * v] = seq[i + j * (j - 1) / 2];
/* in this way we guarantee that the matrix is valid */
matr[j + i * v] = matr[i + j * v];
}
free(seq);

return matr;
}

int *random_sequence(const size_t n, const size_t k, const unsigned int seed)
{
int *seq;
size_t i, s;

if (k > n) exit(1);

/* here we seed the generator used by rand() */
srand(seed);

seq = (int *) calloc(n, sizeof(int));
for (i = 0; i < k; i++) {
do s = rand() % n; while (seq[s] != 0);
seq[s] = 1;
}

return seq;
}

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