CareerCup

C code:

struct Node {
        int i; 
        struct Node* next;
};
int* visited;
void dfsvisit(struct Node** adjlist, int s, struct Node** phead) {
        visited[s] = 1;
        for(struct Node* tmp = adjlist[s]; tmp != 0; tmp = tmp->next)
                if(visited[tmp->i] == 0)
                        dfsvisit(adjlist, tmp->i, phead);
        visited[s] = 2;
        struct Node* nn = (struct Node*)malloc(sizeof(struct Node));
        nn->i = s;
        nn->next = *phead;
        *phead = nn;
}

struct Node* dfs(struct Node** adjlist, int nv) {
        visited = malloc(sizeof(int) * nv);
        for(int i = 0; i < nv; i++)
                visited[i] = 0;
        struct Node* head = 0;
        for(int i = 0; i < nv; i++)
                if(visited[i] == 0)
                        dfsvisit(adjlist, i, &head);
        return head;
}
struct Node* topological_sort(int CV, int CE, int preq[][2]) {
        // adjacency list representation of graph
        struct Node** adjlist = (struct Node**)malloc(sizeof(struct Node*) * CV);
        for(int i = 0; i < CE; i++) {
                struct Node* nn = (struct Node*)malloc(sizeof(struct Node));
                nn->i = preq[i][1];
                nn->next = adjlist[preq[i][0]];
                adjlist[preq[i][0]] = nn;
        }
        // return ordered list of subject
        return dfs(adjlist, CV);
}

Test Code: (warning: this test code may generate cyclic graph, for correct result please pass your acyclic prerequisites to topological_sort function.)

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

int main(int argc, char** argv) {
        int CV = 10;
        int CE = 10;
        if(argc > 1)
                CV = atoi(argv[1]);
        if(argc > 2)
                CE = atoi(argv[2]);
        char (*courses)[CV][100] = malloc(sizeof(*courses));
        for(int i = 0; i < CV; i++)
                sprintf((*courses)[i], "c-%d", i);
        int (*preq)[CE][2] = malloc(sizeof(*preq));
        srand(time(0));
        for(int i = 0; i < CE; i++) {
                (*preq)[i][0] = rand() % CV;
                (*preq)[i][1] = rand() % CV;
        }
        struct Node* orderedlist = topological_sort(CV, CE, *preq);
        printf("ordered courses names list:");
        for(struct Node* tmp = orderedlist; tmp != 0; tmp = tmp->next) {
                printf("->[%s]", (*courses)[tmp->i]);
        }
        printf("\n");
        return 0;
}