[199] 二叉树的右视图

BFS

/*
 * @lc app=leetcode.cn id=199 lang=javascript
 *
 * [199] 二叉树的右视图
 */

// @lc code=start
/**
 * 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) {
    if (root === null) return [];
    let ans = [],
        queue = [root];

    while (queue.length) {
        const len = queue.length;
        ans.push(queue[0].val);

        for (let i = 0; i < len; i++) {
            const item = queue.shift();
            if (item.right !== null) queue.push(item.right);
            if (item.left !== null) queue.push(item.left);
        }
    }
    return ans;
};
// @lc code=end