Binary Tree Right Side View

Problem

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

Solution

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @return {number[]}
 */
var rightSideView = function(root) {
    const queue = root ? [root] : [];
    const res = [];

    while (queue.length) {
        const n = queue.length;
        res.push(queue[n - 1].val);
        for (let i = 0; i < n; i++) {
            const node = queue.shift();

            if (node.left) {
                queue.push(node.left);
            }
            if (node.right) {
                queue.push(node.right);
            }
        }
    }
    return res;
};

We will implement a BFS solution. We do a level order traversal on root, and add the last node of each level to res (ie. the last node is the right view of each level).

Problem​

Solution​

Problem

Solution