层序遍历2

凑数 ......

描述 :

给你二叉树的根节点 root ，返回其节点值 自底向上的层序遍历 。 （即按从叶子节点所在层到根节点所在的层，逐层从左向右遍历）

题目 :

LeetCode 107.二叉树的层序遍历 : 

107. 二叉树的层序遍历 II

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public List> levelOrderBottom(TreeNode root) {
        List> list = new LinkedList<>();
        if(root == null){
            return list;
        }
        Queue queue = new LinkedList<>();
        queue.add(root);

        while(queue.size() > 0){
            List x = new ArrayList<>();
            int num = queue.size();
            for(int i = 1;i <= num ; i++){
                TreeNode temp = queue.remove();
                x.add(temp.val);
                if(temp.left != null){
                    queue.add(temp.left);
                }
                if(temp.right != null){
                    queue.add(temp.right);
                }
            }
            list.add(0,x);
        }


        return list;
    }
}