Define “cyclic data structures”

Question

At the JSON site it says

JSON does not support cyclic data structures, so be careful to not give cyclical structures to the JSON stringifier.

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Answer 1

var cyclic = {};
cyclic.somekey = cyclic;
cyclic.another = "Hello world!";

Now you can do this, for example:

alert(cyclic.somekey.somekey.somekey.another);

Answer 2

A cyclic data structure is a structure that holds a reference to itself (directly or indirectly). See also http://en.wikipedia.org/wiki/Circular_reference

Here is an example of such structure:

var c = { value: 'abc' };
c['c'] = c;
c['a'] = { value: c };

If you try to print its string representation recursively, you will end up with a stack overflow, because to print a value of c you must print the value of c.

Answer 3

CYCLE: A situation in which you return to the same place where you started.

CYCLIC DATA STRUCTURE: A data structure in which such situation might arise. For example graph,linked list (singly/doubly), dequeue, etc.

A linked list node in JS is implemented as:

function Node(data){
    this.data = data;
    this.next = null;
}

Now I create two such nodes as shown below:

var node1 = new Node(10);
var node2 = new Node(20);

And link them to form a cycle.

node1.next = node2;
node2.next = node1;

The following traversal code will enter an infinite loop which shows the existence of a cycle.

node = node1;
while(node!==null){
    print(node.data);
    node = node.next;
}