102.二叉树的层序遍历

层序遍历

class Solution {
    List<List<Integer>> result = new ArrayList<>();
    Queue<TreeNode> que = new LinkedList<>();

    public List<List<Integer>> levelOrder(TreeNode root) {
        if(root != null) que.offer(root);
        while (!que.isEmpty()){
            int len = que.size();
            List<Integer> List = new ArrayList<>();
            
            for(int i = 0;i < len; i++){
                TreeNode tmpNode = que.poll();
                 List.add(tmpNode.val);
                 if (tmpNode.left != null) que.offer(tmpNode.left);// offer():添加
                 if (tmpNode.right != null) que.offer(tmpNode.right);
            }
            result.add(List);
        }
        return result;
    }
}