【LeetCode热题100（44/100）】二叉树的右视图

题目地址：链接

思路： 每层最后一个（层序遍历）最后一个压入数组

/**
 * 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) return [];
    let ans = [];
    let q = [root];
    let ceng = [];

    let last = true;
    while(q.length) {
        let node = q.shift();
        if(!node) continue;

        if(node.left) ceng.push(node.left);
        if(node.right)ceng.push(node.right);
        
        if(q.length == 0) {
            ans.push(node.val);
            q = [...ceng];
            ceng = [];
            last = true;
        }
    }
    return ans;
};