CareerCup

/* O(n) solution to the problem if generator string is "ab" */
char * findpattern(char *str) {
char *tmp;
if (!str || !(*str)) return NULL;
if (*str == 'b') return str;
tmp = str;
do {
tmp = findpattern(tmp+1);
if (!tmp || !(*tmp)) return NULL;
if (*tmp == 'b') tmp++;
} while(*tmp == 'a');
return tmp;
}

int main(void) {
char *op;
char *string = "abbaab";
op = findpattern(string);
if (!op || *op != 0) {
printf("Invalid string\n");
}
else {
printf("Valid string\n");
}
return 0;
}

void fib(int x, int N, int prv1, int prv2) {
if (x<=N) {
fib(x+1, N, prv1+prv2, prv1);
printf("%d\t", prv1+prv2);
}
}

int main(void) {
int Nth = 10; // Starting from 0th to Nth

if (Nth > 1) {
fib(2, Nth, 1, 0);
}
if (Nth > 0) {
printf("1\t"); //1st fib number
}
if (Nth > -1) {
printf("0\t"); //0th fib number
}
return 0;
}

Another solution using 3 pointers,

void reverseNodes(Node ** head)
{
Node* cur, nxt, prv;

cur = *head;

while(cur)
{

if ( !(nxt = cur->next) ) break;

cur->next = nxt->next;
nxt->next = cur;

if ( cur == *head )
{
*head = nxt;
}
else
{
prv->next = nxt;
}

prv = cur;
cur=cur->next;

}//end of while

}// end of reverseNodes