Linked list

1. Check if there is a common node in 2 linked lists.

Solution: All we need to do is to first calculate len=len1-len2 (len1>len2, as discussed above). Point p1 and p2 to list1 (the longer one) and list2 respectively. Then step only p1 for "len" no. of nodes. After this we are guaranteed that p1 and p2 are equidistant from the common node. So now start stepping p1 and p2 simultaneously until p1==p2. This will the common node. This is a simple O(n) solution.