Leetcode刷题-Java版本

1. 623. 在二叉树中增加一行

难度：中等

/**
 * 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) {

        List<TreeNode> pre = new LinkedList<>(),cur = new LinkedList<>();

        if(depth != 1){
            int dep = 1;
            // dep 表示树的深度
            pre.add(root);
            while(!pre.isEmpty()){
                for (TreeNode e : pre) {
                    if(e != null){
                        if(dep + 1 == depth){
                            TreeNode new_left = new TreeNode(val),new_right = new TreeNode(val);;
                            new_left.left = e.left;
                            e.left = new_left;
                            new_right.right = e.right;
                            e.right = new_right;
                        }else{
                            cur.add(e.left);
                            cur.add(e.right);
                        }
                    }
                }
                dep ++;
                pre = new LinkedList<>(cur);
                cur = new LinkedList<>();
            }
        }else{
            TreeNode new_node = new TreeNode(val);
            new_node.left = root;
            root = new_node;
        }

        return root;
    }
}