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Added level order traversal, and more nodes in main method #103

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Merged
merged 3 commits into from
Oct 18, 2017
Merged

Added level order traversal, and more nodes in main method #103

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1e52ba3
Added level order traversal, and more nodes in main method
mpokryva Sep 28, 2017
6823278
Added comments to level order traversal method, and samples in main m…
mpokryva Oct 5, 2017
bb6f827
Merge branch 'master' into level-order
mpokryva Oct 10, 2017
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72 changes: 40 additions & 32 deletions data_structures/Trees/TreeTraversal.java
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Original file line number Diff line number Diff line change
@@ -1,46 +1,50 @@
/**
*
* @author Varun Upadhyay (https://github.com/varunu28)
*
*/
import java.util.LinkedList;

/**
*
* @author Varun Upadhyay (https://github.com/varunu28)
*
*/


// Driver Program
public class TreeTraversal {
public static void main(String[] args) {
Node tree = new Node(5);
tree.insert(3);
tree.insert(2);
tree.insert(7);
tree.insert(1);
tree.insert(9);

// Prints 1 3 5 7 9
tree.printInOrder();
System.out.println();
tree.insert(4);
tree.insert(6);
tree.insert(8);

// Prints 5 3 1 7 9
// Prints 5 3 2 4 7 6 8
System.out.println("Pre order traversal:");
tree.printPreOrder();
System.out.println();

// Prints 1 3 9 7 5
// Prints 2 3 4 5 6 7 8
System.out.println("In order traversal:");
tree.printInOrder();
System.out.println();
// Prints 2 4 3 6 8 7 5
System.out.println("Post order traversal:");
tree.printPostOrder();
System.out.println();

// Add a couple more nodes for print level test
// Print 5 3 7 1 9
// Prints 5 3 7 2 4 6 8
System.out.println("Level order traversal:");
tree.printLevelOrder();
System.out.println();
}
}

/**
* The Node class which initializes a Node of a tree
* Consists of all 3 traversal methods: printInOrder, printPostOrder & printPreOrder
* printInOrder: LEFT -> ROOT -> RIGHT
* printPreOrder: ROOT -> LEFT -> RIGHT
* printPostOrder: LEFT -> RIGHT -> ROOT
* printLevelOrder: ROOT -> ROOT's CHILDREN -> ROOT's CHILDREN's CHILDREN -> etc
*/
* The Node class which initializes a Node of a tree
* Consists of all 3 traversal methods: printInOrder, printPostOrder & printPreOrder
* printInOrder: LEFT -> ROOT -> RIGHT
* printPreOrder: ROOT -> LEFT -> RIGHT
* printPostOrder: LEFT -> RIGHT -> ROOT
* printLevelOrder: Prints by level (starting at root), from left to right.
*/
class Node {
Node left, right;
int data;
Expand Down Expand Up @@ -98,19 +102,23 @@ public void printPostOrder() {
System.out.print(data + " ");
}

/**
* O(n) time algorithm.
* Uses O(n) space to store nodes in a queue to aid in traversal.
*/
public void printLevelOrder() {
LinkedList<Node> queue = new LinkedList<>();
queue.add(this);
while(!queue.isEmpty()) {
Node n = queue.poll();
System.out.print(n.data + " ");
if (n.left != null) {
queue.add(n.left);
while (queue.size() > 0) {
Node head = queue.remove();
System.out.print(head.data + " ");
// Add children of recently-printed node to queue, if they exist.
if (head.left != null) {
queue.add(head.left);
}
if (n.right != null) {
queue.add(n.right);
if (head.right != null) {
queue.add(head.right);
}
}
}
}