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LeetCode solutions

103. Binary Tree Zigzag Level Order Traversal

My accepted JavaScript solution to LeetCode problem 103, Binary Tree Zigzag Level Order Traversal, running in 0ms.

  • Difficulty: Medium
  • JavaScript
  • Runtime 0ms
  • Memory 54.6MB

Read the problem on LeetCode View on GitHub

The problem statement is LeetCode’s and stays on their site. What follows is my accepted solution.

JavaScript

Accepted on LeetCode — runtime 0ms, memory 54.6MB, accepted 2025-12-24.

javascript
/**
 * @param {TreeNode} root
 * @return {number[][]}
 */
var zigzagLevelOrder = function(root) {
    if (!root) return [];
    
    const result = [];
    const queue = [root];
    let leftToRight = true;
    
    while (queue.length > 0) {
        const levelSize = queue.length;
        const level = [];
        
        for (let i = 0; i < levelSize; i++) {
            const node = queue.shift();
            
            if (leftToRight) {
                level.push(node.val);
            } else {
                level.unshift(node.val);
            }
            
            if (node.left) queue.push(node.left);
            if (node.right) queue.push(node.right);
        }
        
        result.push(level);
        leftToRight = !leftToRight;
    }
    
    return result;
};

Source