270t103锯齿遍历二叉树-创新互联

层次遍历,遇到偶数行反转

// 270 t103 锯齿遍历
    public List>zigzagLevelOrder(TreeNode root) {boolean isLeftToR=true;
        Queuequeue= new LinkedList<>();
        ArrayList>res = new ArrayList<>();
        if (root==null){return res;
        }

        queue.offer(root);
        while (!queue.isEmpty()){int len=queue.size();
            ArrayListlist = new ArrayList<>();
            while (len>0){TreeNode poll = queue.poll();
                list.add(poll.val);
                if (poll.left!=null){queue.offer(poll.left);
                }

                if (poll.right!=null){queue.offer(poll.right);
                }
                len--;

            }
            if (!isLeftToR){Collections.reverse(list);
            }
            res.add(list);
            isLeftToR=!isLeftToR;

        }
       
        return res;

    }

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