Read the How to prepare for an interview series at my blog: http://se7so.blogspot.com/2014/01/how-to-prepare-for-interview.html

prob11.cpp

#include "list.h" // See problem #8

node* getLoopStart(node* lst) {
	node *lnk1 = lst, *lnk2 = lst;
	
	while(lnk2->nxt) {
		lnk1 = lnk1->nxt;
		lnk2 = lnk2->nxt->nxt;
		
		if(lnk2 == NULL) return NULL;
		
		if(lnk1 == lnk2)
			break;
	}
	
	if(lnk2->nxt == NULL)
		return NULL;
		
	lnk1 = lst;
	
	while(lnk1 != lnk2) {
		lnk1 = lnk1->nxt;
		lnk2 = lnk2->nxt;
	}
	
	return lnk1;
}