binaryTreeRightSideView.js

/*
Given the root of a binary tree, imagine yourself standing on the right side of it, return the values
of the nodes you can see ordered from top to bottom.

Example 1:
Input: root = [1,2,3,null,5,null,4]
Output: [1,3,4]

Example 2:
Input: root = [1,null,3]
Output: [1,3]

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

Constraints:
    The number of nodes in the tree is in the range [0, 100].
    -100 <= Node.val <= 100
*/

/**
 * @param {TreeNode} root
 * @return {number[]}
 */
function rightSideView(root) {
    if (!root) return [];
    const result = [];
    const queue = [root];

    while (queue.length) {
        const size = queue.length;
        for (let i = 0; i < size; i++) {
            const node = queue.shift();
            if (i === size - 1) result.push(node.val); // last node in level
            if (node.left) queue.push(node.left);
            if (node.right) queue.push(node.right);
        }
    }
    return result;
}

// Helper
function TreeNode(val, left, right) { this.val = val; this.left = left || null; this.right = right || null; }

// Example usage:
const root = new TreeNode(1,
    new TreeNode(2, null, new TreeNode(5)),
    new TreeNode(3, null, new TreeNode(4))
);
console.log(rightSideView(root)); // Output: [1, 3, 4]