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Tree_LevelOrderTraversal.java
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Tree_LevelOrderTraversal.java
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import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;
// https://www.geeksforgeeks.org/level-order-tree-traversal/
// https://practice.geeksforgeeks.org/problems/level-order-traversal/1/
public class Tree_LevelOrderTraversal {
private static List<Integer> levelOrderTraversal(Node root) {
List<Integer> output = new ArrayList<>();
if (root == null) return output;
Queue<Node> queue = new LinkedList<>();
queue.add(root);
while(!queue.isEmpty()) {
Node currNode = queue.poll();
output.add(currNode.data);
if(currNode.left != null) queue.add(currNode.left);
if(currNode.right != null) queue.add(currNode.right);
}
return output;
}
public static void main(String[] args) throws IOException {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
int t = Integer.parseInt(br.readLine().trim());
while (t-- > 0) {
String input = br.readLine().trim();
Node root = buildTree(input);
List<Integer> output = levelOrderTraversal(root);
printTree(output);
}
}
private static void printTree(List<Integer> output) {
StringBuilder sb = new StringBuilder();
for (int value : output) {
sb.append(value).append(" ");
}
System.out.println(sb);
sb.setLength(0);
}
static Node buildTree(String str) {
if (str.length() == 0 || str.charAt(0) == 'N') {
return null;
}
String[] ip = str.split("\\s+");
Node root = new Node(Integer.parseInt(ip[0]));
Queue<Node> queue = new LinkedList<>();
queue.add(root);
int i = 1;
while (!queue.isEmpty() && i < ip.length) {
Node currNode = queue.peek();
queue.remove();
String currVal = ip[i];
if (!currVal.equals("N")) {
currNode.left = new Node(Integer.parseInt(currVal));
queue.add(currNode.left);
}
i++;
if (i >= ip.length) break;
currVal = ip[i];
if (!currVal.equals("N")) {
currNode.right = new Node(Integer.parseInt(currVal));
queue.add(currNode.right);
}
i++;
}
return root;
}
static class Node {
int data;
Node left;
Node right;
Node(int data){
this.data = data;
left = right = null;
}
}
}