37 lines
1.2 KiB
Markdown
37 lines
1.2 KiB
Markdown
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# 32.3 按之字形顺序打印二叉树
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[NowCoder](https://www.nowcoder.com/practice/91b69814117f4e8097390d107d2efbe0?tpId=13&tqId=11212&tPage=1&rp=1&ru=/ta/coding-interviews&qru=/ta/coding-interviews/question-ranking&from=cyc_github)
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## 题目描述
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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。
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## 解题思路
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```java
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public ArrayList<ArrayList<Integer>> Print(TreeNode pRoot) {
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ArrayList<ArrayList<Integer>> ret = new ArrayList<>();
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Queue<TreeNode> queue = new LinkedList<>();
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queue.add(pRoot);
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boolean reverse = false;
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while (!queue.isEmpty()) {
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ArrayList<Integer> list = new ArrayList<>();
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int cnt = queue.size();
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while (cnt-- > 0) {
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TreeNode node = queue.poll();
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if (node == null)
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continue;
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list.add(node.val);
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queue.add(node.left);
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queue.add(node.right);
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}
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if (reverse)
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Collections.reverse(list);
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reverse = !reverse;
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if (list.size() != 0)
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ret.add(list);
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}
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return ret;
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}
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```
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