Traversing of Tree in data structure is done using two method Depth First Search and Breadth First Search
Depth-First Search
Depth-first search is a type of traversal that goes deep as much as possible in every child before exploring the next sibling.
public class BinaryTree {
Node root;
class Node {
int value;
Node left;
Node right;
Node(int value) {
this.value = value;
right = null;
left = null;
}
}
private Node addRecursive(Node current, int value) {
if (current == null) {
return new Node(value);
}
if (value < current.value) {
current.left = addRecursive(current.left, value);
} else if (value > current.value) {
current.right = addRecursive(current.right, value);
} else {
// value already exists
return current;
}
return current;
}
public void add(int value) {
root = addRecursive(root, value);
}
private BinaryTree createBinaryTree() {
BinaryTree bt = new BinaryTree();
bt.add(6);
bt.add(4);
bt.add(8);
bt.add(3);
bt.add(5);
bt.add(7);
bt.add(9);
return bt;
}
private int findSmallestValue(Node root) {
return root.left == null ? root.value : findSmallestValue(root.left);
}
private boolean containsNodeRecursive(Node current, int value) {
if (current == null) {
return false;
}
if (value == current.value) {
return true;
}
return value < current.value
? containsNodeRecursive(current.left, value)
: containsNodeRecursive(current.right, value);
}
public boolean containsNode(int value) {
return containsNodeRecursive(root, value);
}
public void givenABinaryTree_WhenAddingElements_ThenTreeContainsThoseElements() {
BinaryTree bt = createBinaryTree();
assertTrue(bt.containsNode(6));
assertTrue(bt.containsNode(4));
assertFalse(bt.containsNode(1));
}
private Node deleteRecursive(Node current, int value) {
if (current == null) {
return null;
}
if (value == current.value) {
// Case 1: no children
if (current.left == null && current.right == null) {
return null;
}
// Case 2: only 1 child
if (current.right == null) {
return current.left;
}
if (current.left == null) {
return current.right;
}
// Case 3: 2 children
int smallestValue = findSmallestValue(current.right);
current.value = smallestValue;
current.right = deleteRecursive(current.right, smallestValue);
return current;
}
if (value < current.value) {
current.left = deleteRecursive(current.left, value);
return current;
}
current.right = deleteRecursive(current.right, value);
return current;
}
public void delete(int value) {
root = deleteRecursive(root, value);
}
public void traverseInOrder(Node node) {
if (node != null) {
traverseInOrder(node.left);
System.out.print(" " + node.value);
traverseInOrder(node.right);
}
}
public void traversePreOrder(Node node) {
if (node != null) {
System.out.print(" " + node.value);
traversePreOrder(node.left);
traversePreOrder(node.right);
}
}
public void traversePostOrder(Node node) {
if (node != null) {
traversePostOrder(node.left);
traversePostOrder(node.right);
System.out.print(" " + node.value);
}
}
public static void main(String[] args){
BinaryTree bt=new BinaryTree();
bt.givenABinaryTree_WhenAddingElements_ThenTreeContainsThoseElements();
bt.delete();
bt.traverseInOrder(root);
bt.traversePostOrder(root)
}
}
Travering of tree using Breadth-First Search
public class BinaryTree {
Node root;
class Node {
int value;
Node left;
Node right;
Node(int value) {
this.value = value;
right = null;
left = null;
}
}
private Node addRecursive(Node current, int value) {
if (current == null) {
return new Node(value);
}
if (value < current.value) {
current.left = addRecursive(current.left, value);
} else if (value > current.value) {
current.right = addRecursive(current.right, value);
} else {
// value already exists
return current;
}
return current;
}
public void add(int value) {
root = addRecursive(root, value);
}
private BinaryTree createBinaryTree() {
BinaryTree bt = new BinaryTree();
bt.add(6);
bt.add(4);
bt.add(8);
bt.add(3);
bt.add(5);
bt.add(7);
bt.add(9);
return bt;
}
private int findSmallestValue(Node root) {
return root.left == null ? root.value : findSmallestValue(root.left);
}
private boolean containsNodeRecursive(Node current, int value) {
if (current == null) {
return false;
}
if (value == current.value) {
return true;
}
return value < current.value
? containsNodeRecursive(current.left, value)
: containsNodeRecursive(current.right, value);
}
public boolean containsNode(int value) {
return containsNodeRecursive(root, value);
}
public void givenABinaryTree_WhenAddingElements_ThenTreeContainsThoseElements() {
BinaryTree bt = createBinaryTree();
assertTrue(bt.containsNode(6));
assertTrue(bt.containsNode(4));
assertFalse(bt.containsNode(1));
}
private Node deleteRecursive(Node current, int value) {
if (current == null) {
return null;
}
if (value == current.value) {
// Case 1: no children
if (current.left == null && current.right == null) {
return null;
}
// Case 2: only 1 child
if (current.right == null) {
return current.left;
}
if (current.left == null) {
return current.right;
}
// Case 3: 2 children
int smallestValue = findSmallestValue(current.right);
current.value = smallestValue;
current.right = deleteRecursive(current.right, smallestValue);
return current;
}
if (value < current.value) {
current.left = deleteRecursive(current.left, value);
return current;
}
current.right = deleteRecursive(current.right, value);
return current;
}
public void traverseLevelOrder() {
if (root == null) {
return;
}
Queue<Node> nodes = new LinkedList<>();
nodes.add(root);
while (!nodes.isEmpty()) {
Node node = nodes.remove();
System.out.print(" " + node.value);
if (node.left != null) {
nodes.add(node.left);
}
if (node.right != null) {
nodes.add(node.right);
}
}
}
public void delete(int value) {
root = deleteRecursive(root, value);
}
public static void main(String[] args){
BinaryTree bt=new BinaryTree();
bt.givenABinaryTree_WhenAddingElements_ThenTreeContainsThoseElements();
bt.delete();
bt.traverseLevelOrder();
}
}