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ZigZag.java
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114 lines (101 loc) · 3.05 KB
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package CodingPatterns.TreeBFS;
import java.util.ArrayList;
import java.util.Deque;
import java.util.LinkedList;
import java.util.List;
/**
* To implement a zigzag level order traversal of a binary tree in Java,
* you can use a breadth-first search (BFS) approach combined with a deque
* to alternate the order of traversal at each level.
*/
class TreeNode {
/**
* The Value.
*/
int value;
/**
* The Left.
*/
TreeNode left;
/**
* The Right.
*/
TreeNode right;
/**
* Instantiates a new Tree node.
*
* @param value the value
*/
TreeNode(int value) {
this.value = value;
}
}
/**
* The type Zig zag.
*/
public class ZigZag {
/**
* Zig zag level order traversal list.
*
* @param head the head
* @return the list
*/
public static List<List<Integer>> zigZagLevelOrderTraversal(TreeNode head){
List<List<Integer>> zigZag = new ArrayList<>();
if(null == head)
return zigZag;
Deque<TreeNode> deque = new LinkedList<>();
deque.offer(head);
boolean leftToRight = true;
while(!deque.isEmpty()){
int levelSize = deque.size();
List<Integer> currentLevel = new ArrayList<>(levelSize);
for(int i=0;i<levelSize;i++){
if (leftToRight) {
TreeNode currentNode = deque.pollFirst();
currentLevel.add(currentNode.value);
if (currentNode.left != null) {
deque.offerLast(currentNode.left);
}
if (currentNode.right != null) {
deque.offerLast(currentNode.right);
}
} else {
TreeNode currentNode = deque.pollLast();
currentLevel.add(currentNode.value);
if (currentNode.right != null) {
deque.offerFirst(currentNode.right);
}
if (currentNode.left != null) {
deque.offerFirst(currentNode.left);
}
}
}
zigZag.add(currentLevel);
leftToRight = !leftToRight;
}
return zigZag;
}
/**
* The entry point of application.
*
* @param args the input arguments
*/
public static void main(String[] args) {
// Creating the binary tree
TreeNode root = new TreeNode(1);
root.left = new TreeNode(2);
root.right = new TreeNode(3);
root.left.left = new TreeNode(4);
root.left.right = new TreeNode(5);
root.right.left = new TreeNode(6);
root.right.right = new TreeNode(7);
// Get zigzag level order traversal
List<List<Integer>> result = zigZagLevelOrderTraversal(root);
// Print zigzag level order traversal
System.out.println("Zigzag Level Order Traversal:");
for (List<Integer> level : result) {
System.out.println(level);
}
}
}