refactor: remove buildTree (#716)

codes/swift/chapter_tree/binary_search_tree.swift

@@ -10,9 +10,10 @@ import utils
 class BinarySearchTree {
     private var root: TreeNode?
 
-    init(nums: [Int]) {
-        let nums = nums.sorted() // 排序数组
-        root = buildTree(nums: nums, i: 0, j: nums.count - 1) // 构建二叉搜索树
+    /* 构造方法 */
+    init() {
+        // 初始化空树
+        root = nil
     }
 
     /* 获取二叉树根节点 */
@@ -20,20 +21,6 @@ class BinarySearchTree {
         root
     }
 
-    /* 构建二叉搜索树 */
-    func buildTree(nums: [Int], i: Int, j: Int) -> TreeNode? {
-        if i > j {
-            return nil
-        }
-        // 将数组中间节点作为根节点
-        let mid = (i + j) / 2
-        let root = TreeNode(x: nums[mid])
-        // 递归建立左子树和右子树
-        root.left = buildTree(nums: nums, i: i, j: mid - 1)
-        root.right = buildTree(nums: nums, i: mid + 1, j: j)
-        return root
-    }
-
     /* 查找节点 */
     func search(num: Int) -> TreeNode? {
         var cur = root
@@ -154,8 +141,12 @@ enum _BinarySearchTree {
     /* Driver Code */
     static func main() {
         /* 初始化二叉搜索树 */
-        let nums = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
-        let bst = BinarySearchTree(nums: nums)
+        let bst = BinarySearchTree()
+        // 请注意，不同的插入顺序会生成不同的二叉树，该序列可以生成一个完美二叉树
+        let nums = [8, 4, 12, 2, 6, 10, 14, 1, 3, 5, 7, 9, 11, 13, 15]
+        for num in nums {
+            bst.insert(num: num)
+        }
         print("\n初始化的二叉树为\n")
         PrintUtil.printTree(root: bst.getRoot())