Last active
November 3, 2023 16:18
-
-
Save stefanobaghino/7d411ef4d3a2ab548fceeb59f013b784 to your computer and use it in GitHub Desktop.
Shuffle an array
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
#include <stdio.h> | |
#include <stdlib.h> | |
#include <time.h> | |
void shuffle(int array[], size_t n) { | |
if (n > 1) { | |
size_t i; | |
for (i = n - 1; i > 0; i--) { | |
size_t j = rand() % (i + 1); | |
int tmp = array[j]; | |
array[j] = array[i]; | |
array[i] = tmp; | |
} | |
} | |
} | |
void test_uniformity() { | |
int counts[5] = {0, 0, 0, 0, 0}; | |
for (int i = 0; i < 1e8; i++) { | |
// always start from the same array to measure uniformity | |
int ns[] = {1, 2, 3, 4, 5}; | |
shuffle(ns, 5); | |
for (int j = 0; j < 5; j++) { | |
counts[j] += ns[j]; | |
} | |
} | |
int min = counts[0]; | |
int max = counts[0]; | |
for (int i = 0; i < 5; i++) { | |
if (counts[i] < min) { | |
min = counts[i]; | |
} | |
if (counts[i] > max) { | |
max = counts[i]; | |
} | |
} | |
double ratio = (double) max / min; | |
printf("test_uniformity: %f (0 = perfect)\n", ratio - 1); | |
} | |
void test_performance() { | |
struct timespec start_time, end_time; | |
// initialize only once to measure performance | |
int ns[] = {1, 2, 3, 4, 5}; | |
int ops = 1e8; | |
int start = clock(); | |
for (int i = 0; i < ops; i++) { | |
shuffle(ns, 5); | |
} | |
int end = clock(); | |
double sec_tot = (double) (end - start) / CLOCKS_PER_SEC; | |
double nsec_op = sec_tot / ops * 1e9; | |
printf("test_performance: %fns/op (%fs overall)\n", nsec_op, sec_tot); | |
} | |
int main() { | |
srand(time(NULL)); // seed the rng | |
test_uniformity(); | |
test_performance(); | |
return 0; | |
} |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment