Card Shuffling Algorithm

The Algorithm

Step 1: Initialize the cards. For each i in the [0...n-1] range, set card[i] = i.

Step 2 (optional): Seed the random number generator.

Step 3: Let i = 0.

Step 4: Let j = random_number MOD n.

Step 5: Exchange the values of card[i] and card[j].

Step 6: Let i = i + 1. If i is less than n, go to step 4.

Sample Source Code

Here is a sample C function implementing the algorithm:

void shuffle(int *card, int n) {
	int i, j, k;

	for (i = 0; i < n; i++)
		card[i] = i;

	for (i = 0; i < n; i++) {
		j = rand() % n;
		k = card[i];
		card[i] = card[j];
		card[j] = k;
	}
}

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