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linkedListCycles.java
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linkedListCycles.java
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/*
* Assignment: Write a function that returns true if a linked list contains a cycle, or false if it terminates somewhere
*
* Explanation:
*
* Generally, we assume that a linked list will terminate in a null next pointer, as follows:
*
* A -> B -> C -> D -> E -> null
*
* A 'cycle' in a linked list is when traversing the list would result in visiting the same nodes over and over
* This is caused by pointing a node in the list to another node that already appeared earlier in the list. Example:
*
* A -> B -> C
* ^ |
* | v
* E <- D
*
* hasCycle(nodeA); // => true
*
* Constraint 1: Do this in linear time
* Constraint 2: Do this in constant space
* Constraint 3: Do not mutate the original nodes in any way
*/
public class linkedListCycles {
public static class Node {
private Object value;
public Node next;
public Node prev;
public Node(){
next = null;
prev = null;
value = 0;
}
public Node(Object val){
next = null;
prev = null;
value = val;
}
}
public static boolean hasCycle(Node start){
Node i = start;
Node j = start;
while( i != null && j != null ){
i = i.next;
j = j.next.next;
if( i == j ){
return true;
}
}
return false;
}
public static void main(String[] args){
Node n1 = new Node(1);
n1.next = new Node(2);
n1.next.next = new Node(3);
n1.next.next.next = new Node(4);
n1.next.next.next.next = n1;
System.out.println(hasCycle(n1)); // should be true
n1.next.next.next.next = null;
System.out.println(hasCycle(n1)); // should be false
}
}