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PrintTopViewofTree.java
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106 lines (91 loc) · 2.64 KB
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package DataStructures.Trees;// Java program to print top view of Binary tree
import java.util.HashSet;
import java.util.LinkedList;
import java.util.Queue;
// Class for a tree node
class TreeNode {
// Members
int key;
TreeNode left, right;
// Constructor
public TreeNode(int key) {
this.key = key;
left = 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
class QItem {
TreeNode node;
int hd;
public QItem(TreeNode n, int h) {
node = n;
hd = h;
}
}
// Class for a Binary Tree
class Tree {
TreeNode root;
// Constructors
public Tree() {
root = null;
}
public Tree(TreeNode n) {
root = n;
}
// This method prints nodes in top view of binary tree
public void printTopView() {
// base case
if (root == null) {
return;
}
// Creates an empty hashset
HashSet<Integer> set = new HashSet<>();
// Create a queue and add root to it
Queue<QItem> Q = new LinkedList<QItem>();
Q.add(new QItem(root, 0)); // Horizontal distance of root is 0
// Standard BFS or level order traversal loop
while (!Q.isEmpty()) {
// Remove the front item and get its details
QItem qi = Q.remove();
int hd = qi.hd;
TreeNode n = 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)
Q.add(new QItem(n.left, hd - 1));
if (n.right != null)
Q.add(new QItem(n.right, hd + 1));
}
}
}
// Driver class to test above methods
public class PrintTopViewofTree {
public static void main(String[] args) {
/* Create following Binary Tree
1
/ \
2 3
\
4
\
5
\
6*/
TreeNode root = new TreeNode(1);
root.left = new TreeNode(2);
root.right = new TreeNode(3);
root.left.right = new TreeNode(4);
root.left.right.right = new TreeNode(5);
root.left.right.right.right = new TreeNode(6);
Tree t = new Tree(root);
System.out.println("Following are nodes in top view of Binary Tree");
t.printTopView();
}
}