feat: add 108

Author: Blankj

README.md

@@ -30,6 +30,7 @@
 |101|[Symmetric Tree][101]|Tree, Depth-first Search, Breadth-first Search|
 |104|[Maximum Depth of Binary Tree][104]|Tree, Depth-first Search|
 |107|[Binary Tree Level Order Traversal II][107]|Tree, Breadth-first Search|
+|108|[Binary Tree Level Order Traversal II][107]|Tree, Depth-first Search|
 
 
 ## Medium

note/108/README.md

@@ -0,0 +1,57 @@
+# [Convert Sorted Array to Binary Search Tree][title]
+
+## Description
+
+Given an array where elements are sorted in ascending order, convert it to a height balanced BST.
+
+**Tags:** Tree, Depth-first Search
+
+
+## 思路
+
+题意是把一个有序数组转化为一棵二叉搜索树，二叉搜索树具有以下性质：
+
+1. 若任意节点的左子树不空，则左子树上所有节点的值均小于它的根节点的值；
+2. 若任意节点的右子树不空，则右子树上所有节点的值均大于它的根节点的值；
+3. 任意节点的左、右子树也分别为二叉查找树；
+4. 没有键值相等的节点。
+
+所以我们可以用递归来构建一棵二叉搜索树，每次把数组分为两半，把数组中间的值作为其父节点，然后把数组的左右两部分继续构造其左右子树。
+
+
+``` java
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+class Solution {
+    public TreeNode sortedArrayToBST(int[] nums) {
+        if (nums == null || nums.length == 0) return null;
+        return helper(nums, 0, nums.length - 1);
+    }
+
+    private TreeNode helper(int[] nums, int left, int right) {
+        if (left > right) return null;
+        int mid = (left + right) >>> 1;
+        TreeNode node = new TreeNode(nums[mid]);
+        node.left = helper(nums, left, mid - 1);
+        node.right = helper(nums, mid + 1, right);
+        return node;
+    }
+}
+```
+
+
+## 结语
+
+如果你同我一样热爱数据结构、算法、LeetCode，可以关注我GitHub上的LeetCode题解：[awesome-java-leetcode][ajl]
+
+
+
+[title]: https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree
+[ajl]: https://github.com/Blankj/awesome-java-leetcode

project/leetcode/.idea/workspace.xml

@@ -0,0 +1,33 @@
+package com.blankj.easy._108;
+
+
+import com.blankj.structure.TreeNode;
+
+/**
+ * <pre>
+ *     author: Blankj
+ *     blog  : http://blankj.com
+ *     time  : 2017/10/09
+ *     desc  :
+ * </pre>
+ */
+public class Solution {
+    public TreeNode sortedArrayToBST(int[] nums) {
+        if (nums == null || nums.length == 0) return null;
+        return helper(nums, 0, nums.length - 1);
+    }
+
+    private TreeNode helper(int[] nums, int left, int right) {
+        if (left > right) return null;
+        int mid = (left + right) >>> 1;
+        TreeNode node = new TreeNode(nums[mid]);
+        node.left = helper(nums, left, mid - 1);
+        node.right = helper(nums, mid + 1, right);
+        return node;
+    }
+
+    public static void main(String[] args) {
+        Solution solution = new Solution();
+        TreeNode.print(solution.sortedArrayToBST(new int[]{0, 1, 2, 3, 4, 5, 6, 7}));
+    }
+}

project/leetcode/out/production/leetcode/com/blankj/easy/_108/Solution.class

@@ -14,7 +14,7 @@ public class TreeNode {
     public TreeNode left;
     public TreeNode right;
 
-    TreeNode(int x) {
+    public TreeNode(int x) {
         val = x;
     }