From 6bc81647956c53c9c2f2bfb619e0aa65a304eaf5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E6=A2=A6=E5=A2=83=E8=BF=B7=E7=A6=BB?=
 <dreamylost@outlook.com>
Date: Sun, 12 Jul 2020 00:50:36 +0800
Subject: [PATCH] add scala #1008

---
 scala-leetcode/README.md                      |  1 +
 .../io/github/dreamylost/Leetcode_1008.scala  | 45 +++++++++++++++++++
 2 files changed, 46 insertions(+)
 create mode 100644 scala-leetcode/src/main/scala/io/github/dreamylost/Leetcode_1008.scala

diff --git a/scala-leetcode/README.md b/scala-leetcode/README.md
index 399b907e..f8818856 100644
--- a/scala-leetcode/README.md
+++ b/scala-leetcode/README.md
@@ -61,6 +61,7 @@ Leetcode Scala 实现
 * [从叶结点开始的最小字符串](./src/main/scala/io/github/dreamylost/Leetcode_988.scala)
 * [按垂序遍历返回其结点值](./src/main/scala/io/github/dreamylost/Leetcode_987.scala)
 * [最大二叉树 II](./src/main/scala/io/github/dreamylost/Leetcode_998.scala)
+* [先序遍历构造二叉树](./src/main/scala/io/github/dreamylost/Leetcode_1008.scala)
 
 ## 链表
 
diff --git a/scala-leetcode/src/main/scala/io/github/dreamylost/Leetcode_1008.scala b/scala-leetcode/src/main/scala/io/github/dreamylost/Leetcode_1008.scala
new file mode 100644
index 00000000..e50d32e0
--- /dev/null
+++ b/scala-leetcode/src/main/scala/io/github/dreamylost/Leetcode_1008.scala
@@ -0,0 +1,45 @@
+/* Licensed under Apache-2.0 @梦境迷离 */
+package io.github.dreamylost
+
+/**
+  * 1008. 先序遍历构造二叉树
+  *
+  * 返回与给定先序遍历 preorder 相匹配的二叉搜索树（binary search tree）的根结点。
+  *
+  * (回想一下，二叉搜索树是二叉树的一种，其每个节点都满足以下规则，对于 node.left 的任何后代，值总 < node.val，而 node.right 的任何后代，值总 > node.val。
+  * 此外，先序遍历首先显示节点的值，然后遍历 node.left，接着遍历 node.right。）
+  *
+  * @author 梦境迷离 dreamylost
+  * @since 2020-07-12
+  * @version v1.0
+  */
+object Leetcode_1008 extends App {
+
+  val ret = bstFromPreorder(Array(8, 5, 1, 7, 10, 12))
+  println(ret)
+
+  /**
+    * 已知前序序列，找到第一个不满足左子树的节点，作用相当于在中序序列中构造二叉搜索树时计算的mid
+    * 548 ms,100.00%
+    * 51 MB,100.00%
+    *
+    * @param preorder
+    * @return
+    */
+  def bstFromPreorder(preorder: Array[Int]): TreeNode = {
+    def buildSearchTree(values: Array[Int], l: Int, r: Int): TreeNode = {
+      if (l > r) {
+        return null
+      }
+      val root = new TreeNode(values(l))
+      var index = l
+      while (index <= r && preorder(index) <= preorder(l)) index += 1
+      //head已经被使用
+      root.left = buildSearchTree(values, l + 1, index - 1)
+      root.right = buildSearchTree(values, index, r)
+      root
+    }
+
+    buildSearchTree(preorder, 0, preorder.length - 1)
+  }
+}
-- 
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