Finding loop in a singly linked-list

Question

How can I detect that whether a singly linked-list has loop or not?? If it has loop then how to find the point of origination of the loop i.e. the node from which the loop

Answer 1

You can use hash map also to finding whether a link list have loop or not below function uses hash map to find out whether link list have loop or not

    static bool isListHaveALoopUsingHashMap(Link *headLink) {

        map tempMap;
        Link * temp;
        temp = headLink;
        while (temp->next != NULL) {
            if (tempMap.find(temp) == tempMap.end()) {
                tempMap[temp] = 1;
            } else {
                return 0;
            }
            temp = temp->next;
        }
        return 1;
    }

Two pointer method is best approach because time complexity is O(n) Hash Map required addition O(n) space complexity.