# Find Intersectionby Isai Damier, Android Engineer @ Google

```/***************************************************************************
* Author: Isai Damier
* Project: geekviewpoint
* Package: datastructure
*
* Description: A LinkedList is a data structure that allows access
*   to a collection of data using pointers/references. While an
*   array can also be defined as above, LinkedLists and arrays differ
*   in how they are stored in memory and in the operations they
*   allow. Unlike an array that must be stored in a block of memory,
*   the nodes of a LinkedList can be stored anywhere because each
*   node has a reference to the node that succeeds it. Because the
*   nodes are stored so loosely, inserting nodes into a LinkedList
*   is easy; whereas in an array, all the succeeding elements must
*   be shifted. Of course, insertion also means changing the size of
*   the array, which means creating the entire array anew.
*
*   Perhaps the greatest beauty of LinkedList is that it allows
*   accessing an entire sequence of nodes using only one variable:
*   a reference to the first node in the sequence.
*
*   Countless operations can be performed on LinkedLists. Following
*   are a few, ranging from the common to the very interesting.
**************************************************************************/

Node tail = null;

/*****************************************************************
* Time Complexity of Solution:
*   O(n).
*
* Description: Find the node (intersection) where the two given
*
* Technical Details: The idea is that two linked lists form a Y-shaped
*   structure. The structure may be degenerated. As shown below, the use
*   of a hashmap greatly reduces the complexity of the problem.
*
*
*   To keep things simple, we consider t2 and t2 equal iff they both
*   point to the same memory location. A broader definition of
*   equality: Two nodes t2 and t1 are equal if they and their respective
*   sublists are equal.
*****************************************************************/
Map<Node, Boolean> intersect = new HashMap<Node, Boolean>();
for (Node t = head1; null != t; t = t.next) {
intersect.put(t, true);
}
//first duplicate is intersection
for (Node t = head2; null != t; t = t.next) {
if (null != intersect.get(t)) {
return t;
}
}
return null;
}
}```
```public class SinglyLinkedListTest {

/**
* Test of findIntersection method, of class SinglyLinkedList.
*/
@Test
public void testFindIntersection() {
System.out.println("findIntersection");
int[] in_1 = {29, 14, 35, 2, 1, 12, 6, 7, 4, 8, 3, 0, 16, 19, 11};
int[] in_2 = {99, 78, 8, 3, 23};

for (int i = 0; i < in_1.length; i++) {
}
assertEquals(in_1.length, list_1.size());

for (int i = 0; i < in_2.length; i++) {
}
assertEquals(in_2.length, list_2.size());

//set intersection: list_1 and list_2 form a Y at element 6
int exp = 6;
Node found = list_1.find(exp);
assertNotNull(found);