Java/src/main/java/com/thealgorithms/datastructures/trees/PrintTopViewofTree.java at master · TheAlgorithms/Java · GitHub

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packagecom.thealgorithms.datastructures.trees; // Java program to print top view of Binary tree

importjava.util.HashSet;
importjava.util.LinkedList;
importjava.util.Queue;

// Class for a tree node
classTreeNode {

// Members

intkey;
TreeNodeleft;
TreeNoderight;

// Constructor
TreeNode(intkey) {
this.key = key;
left = null;
right = null;
 }
}

// A class to represent a queue item. The queue is used to do Level
// order traversal. Every Queue item contains node and horizontal
// distance of node from root
classQItem {

TreeNodenode;
inthd;

QItem(TreeNoden, inth) {
node = n;
hd = h;
 }
}

// Class for a Binary Tree
classTree {

TreeNoderoot;

// Constructors
Tree() {
root = null;
 }

Tree(TreeNoden) {
root = n;
 }

// This method prints nodes in top view of binary tree
publicvoidprintTopView() {
// base case
if (root == null) {
return;
 }

// Creates an empty hashset
HashSet<Integer> set = newHashSet<>();

// Create a queue and add root to it
Queue<QItem> queue = newLinkedList<QItem>();
queue.add(newQItem(root, 0)); // Horizontal distance of root is 0

// Standard BFS or level order traversal loop
while (!queue.isEmpty()) {
// Remove the front item and get its details
QItemqi = queue.remove();
inthd = qi.hd;
TreeNoden = qi.node;

// If this is the first node at its horizontal distance,
// then this node is in top view
if (!set.contains(hd)) {
set.add(hd);
System.out.print(n.key + " ");
 }

// Enqueue left and right children of current node
if (n.left != null) {
queue.add(newQItem(n.left, hd - 1));
 }
if (n.right != null) {
queue.add(newQItem(n.right, hd + 1));
 }
 }
 }
}

// Driver class to test above methods
publicfinalclassPrintTopViewofTree {
privatePrintTopViewofTree() {
 }

publicstaticvoidmain(String[] args) {
/* Create following Binary Tree
 1
 / \
 2 3
 \
 4
 \
 5
 \
 6*/
TreeNoderoot = newTreeNode(1);
root.left = newTreeNode(2);
root.right = newTreeNode(3);
root.left.right = newTreeNode(4);
root.left.right.right = newTreeNode(5);
root.left.right.right.right = newTreeNode(6);
Treet = newTree(root);
System.out.println("Following are nodes in top view of Binary Tree");
t.printTopView();
 }
}