剑指Offer32,从上到下打印二叉树

Posted 2021-11-23 小布丁value

从上到下打印出二叉树

https://leetcode-cn.com/problems/cong-shang-dao-xia-da-yin-er-cha-shu-lcof/solution/mian-shi-ti-32-i-cong-shang-dao-xia-da-yin-er-ch-4/

public int[] levelOrder(TreeNode root){
        if(root==null) return new int[0];
        List<Integer> list=new ArrayList<>();
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        while(!queue.isEmpty()){
            TreeNode node=queue.poll();
            list.add(node.val);
            if(node.left!=null){
                queue.add(node.left);
            }if(node.right!=null){
                queue.add(node.right);

            }
        }
        Integer [] arr=list.toArray(new Integer[list.size()]);
        int res[]=new int[arr.length];
        for(int i=0;i<res.length;i++){
            res[i]=arr[i];
        }
        return res;
    }