# 32.3 按之字形顺序打印二叉树

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## 题目描述

请实现一个函数按照之字形打印二叉树,即第一行按照从左到右的顺序打印,第二层按照从右至左的顺序打印,第三行按照从左到右的顺序打印,其他行以此类推。

## 解题思路

```java
public ArrayList<ArrayList<Integer>> Print(TreeNode pRoot) {
    ArrayList<ArrayList<Integer>> ret = new ArrayList<>();
    Queue<TreeNode> queue = new LinkedList<>();
    queue.add(pRoot);
    boolean reverse = false;
    while (!queue.isEmpty()) {
        ArrayList<Integer> list = new ArrayList<>();
        int cnt = queue.size();
        while (cnt-- > 0) {
            TreeNode node = queue.poll();
            if (node == null)
                continue;
            list.add(node.val);
            queue.add(node.left);
            queue.add(node.right);
        }
        if (reverse)
            Collections.reverse(list);
        reverse = !reverse;
        if (list.size() != 0)
            ret.add(list);
    }
    return ret;
}
```






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