题解 | #从上往下打印二叉树#

/* function TreeNode(x) {
    this.val = x;
    this.left = null;
    this.right = null;
} */
function PrintFromTopToBottom(root) {
    let res = [];
    if (root === null) return res;
    let queue = [root];

    while (queue.length > 0) {
        let node = queue.shift(); 
        if (node !== null) {
            res.push(node.val);
            queue.push(node.left); 
            queue.push(node.right); 
        }
    }
    return res;
}
module.exports = {
    PrintFromTopToBottom: PrintFromTopToBottom,
};

用队列来实现广度优先搜索（BFS）的方式来遍历树