二叉树遍历框架。

> [东哥带你刷二叉树（纲领篇）](https://labuladong.github.io/algo/1/4/)
> [一套拳法👊刷掉n个遍历树的问题](https://leetcode.cn/problems/convert-bst-to-greater-tree/solution/yi-tao-quan-fa-shua-diao-nge-bian-li-shu-de-wen-5/)


### 题解
1. [144. 二叉树的前序遍历](https://leetcode.cn/problems/binary-tree-preorder-traversal/)
2. [94. 二叉树的中序遍历](https://leetcode.cn/problems/binary-tree-inorder-traversal/)
3. [145. 二叉树的后序遍历](https://leetcode.cn/problems/binary-tree-postorder-traversal/)
4. [589. N 叉树的前序遍历](https://leetcode.cn/problems/n-ary-tree-preorder-traversal/)
5. [590. N 叉树的后序遍历](https://leetcode.cn/problems/n-ary-tree-postorder-traversal/)

#### 延伸扩展
> 中序遍历
> **二叉搜索树的中序遍历**是升序的。
1. [98. 验证二叉搜索树](https://leetcode.cn/problems/validate-binary-search-tree/)
2. [99. 恢复二叉搜索树](https://leetcode.cn/problems/recover-binary-search-tree/)
3. [108. 将有序数组转换为二叉搜索树](https://leetcode.cn/problems/convert-sorted-array-to-binary-search-tree/)
4. [109. 有序链表转换二叉搜索树](https://leetcode.cn/problems/convert-sorted-list-to-binary-search-tree/)
5. [501. 二叉搜索树中的众数](https://leetcode.cn/problems/find-mode-in-binary-search-tree/)
6. [1382. 将二叉搜索树变平衡](https://leetcode.cn/problems/balance-a-binary-search-tree/)
7. [173. 二叉搜索树迭代器](https://leetcode.cn/problems/binary-search-tree-iterator/)
8. [230. 二叉搜索树中第K小的元素](https://leetcode.cn/problems/kth-smallest-element-in-a-bst/)
9. [530. 二叉搜索树的最小绝对差](https://leetcode.cn/problems/minimum-absolute-difference-in-bst/)
10. [671. 二叉树中第二小的节点](https://leetcode.cn/problems/second-minimum-node-in-a-binary-tree/)
11. [783. 二叉搜索树节点最小距离](https://leetcode.cn/problems/minimum-distance-between-bst-nodes/)
12. [897. 递增顺序搜索树](https://leetcode.cn/problems/increasing-order-search-tree/)
13. [653. 两数之和 IV - 输入 BST](https://leetcode.cn/problems/two-sum-iv-input-is-a-bst/)
14. [1305. 两棵二叉搜索树中的所有元素](https://leetcode.cn/problems/all-elements-in-two-binary-search-trees/)
> 后序遍历
15. [104. 二叉树的最大深度](https://leetcode.cn/problems/maximum-depth-of-binary-tree/)
16. [110. 平衡二叉树](https://leetcode.cn/problems/balanced-binary-tree/)
17. [114. 二叉树展开为链表](https://leetcode.cn/problems/flatten-binary-tree-to-linked-list/)
18. [124. 二叉树中的最大路径和](https://leetcode.cn/problems/binary-tree-maximum-path-sum/)
19. [508. 出现次数最多的子树元素和](https://leetcode.cn/problems/most-frequent-subtree-sum/)
20. [543. 二叉树的直径](https://leetcode.cn/problems/diameter-of-binary-tree/)
21. [563. 二叉树的坡度](https://leetcode.cn/problems/binary-tree-tilt/)
22. [687. 最长同值路径](https://leetcode.cn/problems/longest-univalue-path/)
23. [814. 二叉树剪枝](https://leetcode.cn/problems/binary-tree-pruning/)
24. [1325. 删除给定值的叶子节点](https://leetcode.cn/problems/delete-leaves-with-a-given-value/)
25. [979. 在二叉树中分配硬币](https://leetcode.cn/problems/distribute-coins-in-binary-tree/)
26. [865. 具有所有最深节点的最小子树](https://leetcode.cn/problems/smallest-subtree-with-all-the-deepest-nodes/)
27. [1339. 分裂二叉树的最大乘积](https://leetcode.cn/problems/maximum-product-of-splitted-binary-tree/)
28. [1372. 二叉树中的最长交错路径](https://leetcode.cn/problems/longest-zigzag-path-in-a-binary-tree/)
29. [1373. 二叉搜索子树的最大键值和](https://leetcode.cn/problems/maximum-sum-bst-in-binary-tree/)
> 前后序遍历
30. [112. 路径总和](https://leetcode.cn/problems/path-sum/)
31. [113. 路径总和 II](https://leetcode.cn/problems/path-sum-ii/)
32. [129. 求根节点到叶节点数字之和](https://leetcode.cn/problems/sum-root-to-leaf-numbers/)
33. [235. 二叉搜索树的最近公共祖先](https://leetcode.cn/problems/lowest-common-ancestor-of-a-binary-search-tree/)
34. [236. 二叉树的最近公共祖先](https://leetcode.cn/problems/lowest-common-ancestor-of-a-binary-tree/)
35. [257. 二叉树的所有路径](https://leetcode.cn/problems/binary-tree-paths/)
36. [513. 找树左下角的值](https://leetcode.cn/problems/find-bottom-left-tree-value/)
37. [988. 从叶结点开始的最小字符串](https://leetcode.cn/problems/smallest-string-starting-from-leaf/)
38. [938. 二叉搜索树的范围和](https://leetcode.cn/problems/range-sum-of-bst/)
39. [1080. 根到叶路径上的不足节点](https://leetcode.cn/problems/insufficient-nodes-in-root-to-leaf-paths/)
> 前序遍历
40. [100. 相同的树](https://leetcode.cn/problems/same-tree/)
41. [572. 另一棵树的子树](https://leetcode.cn/problems/subtree-of-another-tree/)
42. [101. 对称二叉树](https://leetcode.cn/problems/symmetric-tree/)
43. [104. 二叉树的最大深度](https://leetcode.cn/problems/maximum-depth-of-binary-tree/)
44. [111. 二叉树的最小深度](https://leetcode.cn/problems/minimum-depth-of-binary-tree/)
45. [559. N 叉树的最大深度](https://leetcode.cn/problems/maximum-depth-of-n-ary-tree/)
46. [404. 左叶子之和](https://leetcode.cn/problems/sum-of-left-leaves/)
47. [1022. 从根到叶的二进制数之和](https://leetcode.cn/problems/sum-of-root-to-leaf-binary-numbers/)
48. [515. 在每个树行中找最大值](https://leetcode.cn/problems/find-largest-value-in-each-tree-row/)
49. [623. 在二叉树中增加一行](https://leetcode.cn/problems/add-one-row-to-tree/)
50. [662. 二叉树最大宽度](https://leetcode.cn/problems/maximum-width-of-binary-tree/)
51. [1261. 在受污染的二叉树中查找元素](https://leetcode.cn/problems/find-elements-in-a-contaminated-binary-tree/)
52. [226. 翻转二叉树](https://leetcode.cn/problems/invert-binary-tree/)
53. [951. 翻转等价二叉树](https://leetcode.cn/problems/flip-equivalent-binary-trees/)
54. [700. 二叉搜索树中的搜索](https://leetcode.cn/problems/search-in-a-binary-search-tree/)
55. [971. 翻转二叉树以匹配先序遍历](https://leetcode.cn/problems/flip-binary-tree-to-match-preorder-traversal/)
56. [1026. 节点与其祖先之间的最大差值](https://leetcode.cn/problems/maximum-difference-between-node-and-ancestor/)
57. [1110. 删点成林](https://leetcode.cn/problems/delete-nodes-and-return-forest/)
58. [1302. 层数最深叶子节点的和](https://leetcode.cn/problems/deepest-leaves-sum/)
59. [617. 合并二叉树](https://leetcode.cn/problems/merge-two-binary-trees/)
60. [669. 修剪二叉搜索树](https://leetcode.cn/problems/trim-a-binary-search-tree/)
61. [1379. 找出克隆二叉树中的相同节点](https://leetcode.cn/problems/find-a-corresponding-node-of-a-binary-tree-in-a-clone-of-that-tree/)
62. [987. 二叉树的垂序遍历](https://leetcode.cn/problems/vertical-order-traversal-of-a-binary-tree/)
63. [965. 单值二叉树](https://leetcode.cn/problems/univalued-binary-tree/)
> 反序中序遍历
64. [199. 二叉树的右视图](https://leetcode.cn/problems/binary-tree-right-side-view/)
65. [538. 把二叉搜索树转换为累加树](https://leetcode.cn/problems/convert-bst-to-greater-tree/)
66. [1038. 从二叉搜索树到更大和树](https://leetcode.cn/problems/binary-search-tree-to-greater-sum-tree/)
> 构造二叉树
67. [105. 从前序与中序遍历序列构造二叉树](https://leetcode.cn/problems/construct-binary-tree-from-preorder-and-inorder-traversal/)
68. [106. 从中序与后序遍历序列构造二叉树](https://leetcode.cn/problems/construct-binary-tree-from-inorder-and-postorder-traversal/)
69. [654. 最大二叉树](https://leetcode.cn/problems/maximum-binary-tree/)
70. [889. 根据前序和后序遍历构造二叉树](https://leetcode.cn/problems/construct-binary-tree-from-preorder-and-postorder-traversal/)
71. [1008. 前序遍历构造二叉搜索树](https://leetcode.cn/problems/construct-binary-search-tree-from-preorder-traversal/)


### 1.「遍历」的思维模式
```
    // 记录结果
    private List<Integer> res = new LinkedList<>();

    /**
     * 二叉树遍历框架，「遍历」的思维模式。
     * 非线性递归遍历结构
     */
    private void traverse(TreeNode root) {
        if (root == null) {
            return;
        }
        // 前序位置，添加结果
        res.add(root.val);
        traverse(root.left);
        // // 中序位置，添加结果
        // res.add(root.val);
        traverse(root.right);
        // // 后序位置，添加结果
        // res.add(root.val);
    }
```


学习分享

二叉树遍历框架。

东哥带你刷二叉树（纲领篇）


 题解







 延伸扩展

中序遍历
二叉搜索树的中序遍历是升序的。


















后序遍历



















前后序遍历














前序遍历