一、题目地址

https://www.nowcoder.com/practice/a9fec6c46a684ad5a3abd4e365a9d362?tpId=188&&tqId=38560&rp=1&ru=/activity/oj&qru=/ta/job-code-high-week/question-ranking

二、具体代码

/*
 * function TreeNode(x) {
 *   this.val = x;
 *   this.left = null;
 *   this.right = null;
 * }
 */

/**
 * 
 * @param root TreeNode类 the root of binary tree
 * @return int整型二维数组
 */
function threeOrders( root ) {
    let pre = [];//前序遍历后的结果
    let mid = [];//中序遍历后的结果
    let after = [];//后续遍历后的结果
    let res = [];//结果数组
    //1、前序遍历函数：根前
    let preOrder = function(root) {
        if(root === null) {
            return [];
        }
        pre.push(root.val);
        preOrder(root.left);
        preOrder(root.right);
    }
    //2、中序遍历函数：根中
    let midOrder = function(root) {
       if(root === null) {
           return [];
       }
       midOrder(root.left);
       mid.push(root.val);
       midOrder(root.right);
    }
    //3、后续遍历函数：根后
    let afterOrder = function(root) {
        if(root === null) {
            return [];
        }
        afterOrder(root.left);
        afterOrder(root.right);
        after.push(root.val);
    }
    //4、遍历函数调用
    preOrder(root);
    midOrder(root);
    afterOrder(root);
    //5、返回结果数组
    res.push(pre, mid, after);
    return res;
}
module.exports = {
    threeOrders : threeOrders
};