题解 | #二叉树的前序遍历#

/*
 * function TreeNode(x) {
 *   this.val = x;
 *   this.left = null;
 *   this.right = null;
 * }
 */
/**
 * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
 *
 *
 * @param root TreeNode类
 * @return int整型一维数组
 */
function preorderTraversal(root) {
    // write code here
    let res = [];
    if (root == null) {
        return [];
    }
    res.push(root.val);
    let lefts = preorderTraversal(root.left);
    if (lefts!==null) {
        res.push(...lefts);
    }
    let rights = preorderTraversal(root.right);
    if (rights!==null) {
        res.push(...rights);
    }
    return res
}
module.exports = {
    preorderTraversal: preorderTraversal,
};