cards.c

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>

typedef struct card {
    unsigned int value;
    struct card *next;
} Card_t;

static int AllocateCards(unsigned int numCards, Card_t **deckHead, Card_t **deckTail) {

	unsigned int i;
    for(i = numCards; i != 0; i--) {
    	Card_t *card = malloc(sizeof(Card_t));
    	card->value = i;
    	card->next = *deckHead;
    	*deckHead = card;

    	if(i == numCards) {
    		*deckTail = card;
    	}
    }

    return 0;
}


static int FreeCards(Card_t **deckHead) {

	while(*deckHead != NULL) {
		Card_t *temp = *deckHead;
		*deckHead = *(deckHead->next);
		free(temp);
	}
}

static bool CheckCardOrder(Card_t *deckHead) {

	unsigned int i = 1;
	bool match = true;
	while(deckHead != NULL) {
		if(deckHead->value != i) {
			match = false;
			break;
		}
		i++;
		deckHead = deckHead->next;
	}

	return match;
}

int main(int argc, char **argv) {

    unsigned int numCards;
    if(argc != 2) {
        printf("Error: Incorrect number of command line arguments\n");
        return 1;
    }

    if(sscanf(argv[1], "%i", &numCards) != 1) {
        printf("Error: Command line argument is not an integer\n");
        return 1;
    }

    Card_t *deckHead = NULL;
    Card_t *deckTail = NULL;
    int status = AllocateCards(numCards, &deckHead, &deckTail);

    Card_t *tableHead = NULL;
    Card_t *tableTail = NULL;

    bool match = false;
    unsigned int rounds = 0;
    while(!match) {

    	// Cycle through deck, stop once all cards are on table
        while(deckHead != NULL) {

        	// Putting card on table
        	if(tableHead == NULL) {
        		tableHead = deckHead;
        	}
        	if(tableTail == NULL) {
        		tableTail = deckHead;
        	} else {
        		tableTail->next = deckHead;
        		tableTail = deckHead;
        	}

        	deckHead = deckHead->next;
        	tableTail->next = NULL;

        	// Exit if that was last card
        	if(deckHead == NULL) {
        		break;
        	}

        	// Putting card at bottom of deck
        	deckTail->next = deckHead;
        	deckHead = deckHead->next;
        	deckTail = deckTail->next;
        	deckTail->next = NULL;
        }

        rounds++;
        match = CheckCardOrder(tableHead);

        // Table is not in correct order, need to perform another round. Reset deck
        if(!match) {
        	deckHead = tableHead;
        	deckTail = tableTail;
        	tableHead = NULL;
        	tableTail = NULL;
        }
    }

    FreeCards(tableHead);
    printf("%d", rounds);

    return 0;

}