LeetCode Add One Row to Tree

Given the root of a binary tree, then value v and depth d, you need to add a row of nodes with value v at the given depth d. The root node is at depth 1. 

The adding rule is: given a positive integer depth d, for each NOT null tree nodes N in depth d-1, create two tree nodes with value v as N's left subtree root and right subtree root. And N's original left subtree should be the left subtree of the new left subtree root, its original right subtree should be the right subtree of the new right subtree root. If depth d is 1 that means there is no depth d-1 at all, then create a tree node with value v as the new root of the whole original tree, and the original tree is the new root's left subtree.

Example 1:

Input: A binary tree as following:       4     /   \    2     6   / \   /   3   1 5   v = 1d = 2Output:        4      / \     1   1    /     \   2       6  / \     /  3   1   5   

Example 2:

Input: A binary tree as following:      4     /       2       / \     3   1    v = 1d = 3Output:       4     /       2   / \      1   1 /     \  3       1

Note:

1. The given d is in range [1, maximum depth of the given tree + 1].
2. The given binary tree has at least one tree node.

题解：此题就是给定一个v和d，分别表示需要添加的那一行的值和深度，注意此深度d的范围是从[1,树高+1]，也就是可以表示建立新的根节点，也可以表示新建立一行叶子节点。那么我考虑采用层次遍历方法，用一个对列保存需要添加新一行的深度的上一行，然后依次对这一行的每个节点的左右子树进行操作，会发现，需要将添加的上一行的某个节点原来的左子树赋给新添加的节点，然后将新添加的节点的左子树赋予原来节点的左子树，对于右子树而言，也是如此。这里的层次遍历内循环用了for，而不是我平时常用的while，也是耳目一新，可以看到所控制的树高，所以非常方便。

public class addOneRow{    public TreeNode addOneRow(TreeNode root,int v,int d)    {        if(d == 1)        {            TreeNode newroot = new TreeNode(v);            newroot.left =root;            return newroot;        }        Queue<TreeNode> queue = new LinkedList<>();        queue.add(root);        for(int i = 0; i < d - 2; i++)    //用for循环来层次遍历，得到所要添加的深度的上一层的所有节点，并将结果保存在一个queue队列里        {            int size = queue.size();            for(int j = 0; j < size; j++)            {                TreeNode t = queue.poll();                if(t.left != null)                    queue.add(t.left);                if(t.right != null)                    queue.add(t.right);            }        }        while(!queue.isEmpty())    //对保存有需要添加深度的上一层所有节点的队列，我们依次对每一个节点添加新的节点，并将每一个节点原来的左右子树赋给新添加节点的左右子树        {            TreeNode t = queue.poll();            TreeNode newparent1 = new TreeNode(v);            TreeNode tmp = t.left;            t.left = newparent1;            newparent1.left = tmp;            TreeNode newparent2 = new TreeNode(v);            tmp = t.right;            t.right = newparent2;            newparent2.right = tmp;        }        return root;    }}