Here, We see Binary Tree Zigzag Level Order Traversal LeetCode Solution. This Leetcode problem is done in many programming languages like C++, Java, JavaScript, Python, etc. with different approaches.

List of all LeetCode Solution

Binary Tree Zigzag Level Order Traversal LeetCode Solution

Problem Statement

Given the root of a binary tree, return the zigzag level order traversal of its nodes’ values. (i.e., from left to right, then right to left for the next level and alternate between).

Example 1:

Input: root = [3,9,20,null,null,15,7]
Output: [[3],[20,9],[15,7]]

Example 2:
Input: root = [1]
Output: [[1]]

Example 3:
Input: root = []
Output: []

Binary Tree Zigzag Level Order Traversal LeetCode Solution C++

class Solution {
public:
    vector<vector<int> > zigzagLevelOrder(TreeNode* root) {
        if (root == NULL) {
            return vector<vector<int> > ();
        }
        vector<vector<int> > result;
        queue<TreeNode*> nodesQueue;
        nodesQueue.push(root);
        bool leftToRight = true;
        while ( !nodesQueue.empty()) {
            int size = nodesQueue.size();
            vector<int> row(size);
            for (int i = 0; i < size; i++) {
                TreeNode* node = nodesQueue.front();
                nodesQueue.pop();
                int index = (leftToRight) ? i : (size - 1 - i);
                row[index] = node->val;
                if (node->left) {
                    nodesQueue.push(node->left);
                }
                if (node->right) {
                    nodesQueue.push(node->right);
                }
            }
            leftToRight = !leftToRight;
            result.push_back(row);
        }
        return result;
    }
};Code language: PHP (php)

Binary Tree Zigzag Level Order Traversal LeetCode Solution Java

public class Solution {
    public List<List<Integer>> zigzagLevelOrder(TreeNode root) 
    {
        List<List<Integer>> sol = new ArrayList<>();
        travel(root, sol, 0);
        return sol;
    }
    
    private void travel(TreeNode curr, List<List<Integer>> sol, int level)
    {
        if(curr == null) return;
        if(sol.size() <= level)
        {
            List<Integer> newLevel = new LinkedList<>();
            sol.add(newLevel);
        }
        List<Integer> collection  = sol.get(level);
        if(level % 2 == 0) collection.add(curr.val);
        else collection.add(0, curr.val);
        travel(curr.left, sol, level + 1);
        travel(curr.right, sol, level + 1);
    }
}Code language: PHP (php)

Binary Tree Zigzag Level Order Traversal Solution JavaScript

var zigzagLevelOrder = function(root) {
    if(!root) return [];
    let queue = [root];
    let output = [];
    let deep = 0;
    while(queue.length > 0){
        const size = queue.length;
        const level = [];
        for(let i=0; i< size; i++){
        const node = queue.shift();
        if(deep % 2 == 0) level.push(node.val);
        else level.unshift(node.val);
        if(node.left) queue.push(node.left)
        if(node.right) queue.push(node.right)
        }
        output.push(level)
        deep++;
    }
    return output
};Code language: JavaScript (javascript)

Binary Tree Zigzag Level Order Traversal Solution Python

class Solution(object):
    def zigzagLevelOrder(self, root):
	if not root: return []
	queue = collections.deque([root])
	res = []
	even_level = False
	while queue:
		n = len(queue)
		level = []
		for _ in range(n):
			node = queue.popleft()
			level.append(node.val)
			if node.left:
				queue.append(node.left)
			if node.right:
				queue.append(node.right)
		if even_level:
			res.append(level[::-1])
		else:
			res.append(level)
		even_level = not even_level
	return res