623. 在二叉树中增加一行

题目描述

注意，根节点 root 位于深度 1 。

加法规则如下:

• 给定整数 depth，对于深度为 depth - 1 的每个非空树节点 cur ，创建两个值为 val 的树节点作为 cur 的左子树根和右子树根。
• cur 原来的左子树应该是新的左子树根的左子树。
• cur 原来的右子树应该是新的右子树根的右子树。
• 如果 depth == 1 意味着 depth - 1 根本没有深度，那么创建一个树节点，值 val 作为整个原始树的新根，而原始树就是新根的左子树。

示例 1:

输入: root = [4,2,6,3,1,5], val = 1, depth = 2
输出: [4,1,1,2,null,null,6,3,1,5]

示例 2:

输入: root = [4,2,null,3,1], val = 1, depth = 3
输出: [4,2,null,1,1,3,null,null,1]

提示:

• 节点数在 [1, 104] 范围内
• 树的深度在 [1, 104]范围内
• -100 <= Node.val <= 100
• -105 <= val <= 105
• 1 <= depth <= the depth of tree + 1

coding

1.深度优先

/** * 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 {
    

    int val;
    int depth;
    
    public TreeNode addOneRow(TreeNode root, int val, int depth) {
    
        this.val = val;
        this.depth = depth;
        if(depth == 1){
    
            return new TreeNode(val, root, null);
        }
        dfs(root, 1);
        return root;
        
    }
    
    public void dfs(TreeNode node, int curDepth){
    
        if(curDepth == depth - 1){
    
            if(node != null){
    
                node.left = new TreeNode(val, node.left, null);
                node.right = new TreeNode(val, null, node.right);
            }
            return;
        }
        if (node != null){
    
            dfs(node.left, curDepth + 1);
            dfs(node.right, curDepth + 1);  
        }
       
    }
}

2.广度优先

/** * 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 TreeNode addOneRow(TreeNode root, int val, int depth) {
    
        if(depth == 1){
    
            return new TreeNode(val, root, null);
        }
        List<TreeNode> temp1 = new ArrayList<>();
        temp1.add(root);
        for (int i = 1; i < depth - 1; i ++) {
    
            List<TreeNode> temp2 = new ArrayList<>();
            for(TreeNode node : temp1) {
    
                if (node.left != null) {
    
                    temp2.add(node.left);
                }
                if (node.right != null) {
    
                    temp2.add(node.right);
                }
            }
            temp1 = temp2;
        }
        for(TreeNode node : temp1) {
    
            node.left = new TreeNode(val, node.left, null);
            node.right = new TreeNode(val, null, node.right);
        }
        return root;
        
    }
}