scala leetcode 538

scala-leetcode/README.md

@@ -30,6 +30,7 @@ Leetcode Scala 实现
 * [二叉搜索树中的众数](./src/main/scala/io/github/dreamylost/Leetcode_501.scala)
 * [二叉搜索树的最小绝对差](./src/main/scala/io/github/dreamylost/Leetcode_530.scala)
 * [二叉树的堂兄弟节点](./src/main/scala/io/github/dreamylost/Leetcode_993.scala)
+* [把二叉搜索树转换为累加树](./src/main/scala/io/github/dreamylost/Leetcode_538.scala)
 
 ## 链表
 

scala-leetcode/src/main/scala/io/github/dreamylost/Leetcode_538.scala

+package io.github.dreamylost
+
+/**
+  * 538. 把二叉搜索树转换为累加树
+  *
+ * 给定一个二叉搜索树（Binary Search Tree），把它转换成为累加树（Greater Tree)，使得每个节点的值是原来的节点值加上所有大于它的节点值之和。
+  *
+ * @author 梦境迷离 dreamylost
+  * @since 2020-06-12
+  * @version v1.0
+  */
+object Leetcode_538 extends App {
+
+  val ret = convertBST2(TreeNodeData.treeData3_4())
+  println(ret.left.value)
+  println(ret.value)
+  println(ret.right.value)
+
+  /**
+    * 3292 ms,10.00%
+    * 59.7 MB,100.00%
+    * 函数式写法，仅供参考，很慢
+    *
+   * @param root
+    * @return
+    */
+  def convertBST(root: TreeNode): TreeNode = {
+    var values = Seq[Int]()
+
+    def helper(root: TreeNode)(node: TreeNode => Unit): Unit = {
+      if (root == null) return
+      helper(root.left)(node)
+      node(root)
+      helper(root.right)(node)
+    }
+
+    //1.对于搜索树，记录中序值，大于当前节点即排在当前节点后面的值
+    helper(root) { cur =>
+      if (cur != null) {
+        values = values ++ Seq(cur.value)
+      }
+    }
+
+    //2.对于有序数组，取当前节点后面的所有节点的总和
+    helper(root) { cur =>
+      val gtSum = values.takeRight(values.length - values.indexOf(cur.value) - 1).sum
+      cur.value = cur.value + gtSum
+    }
+
+    root
+  }
+
+  /**
+    * 反过来遍历搜索树，将已遍历的节点的和加到当前节点值上
+    *
+   * 快一倍
+    * 1740 ms,20.00%
+    * 59 MB,100.00%
+    *
+   * @param root
+    * @return
+    */
+  def convertBST2(root: TreeNode): TreeNode = {
+    var num = 0
+
+    def BST(r: TreeNode): Unit = {
+      if (r == null) return
+      BST(r.right)
+      r.value = r.value + num
+      num = r.value
+      BST(r.left)
+    }
+
+    BST(root)
+    root
+  }
+}

scala-leetcode/src/main/scala/io/github/dreamylost/TreeNodeData.scala

@@ -49,6 +49,16 @@ object TreeNodeData {
     root
   }
 
+  //搜索树
+  def treeData3_4(): TreeNode = {
+    val root = new TreeNode(2)
+    val r1 = new TreeNode(3)
+    val l1 = new TreeNode(1)
+    root.right = r1
+    root.left = l1
+    root
+  }
+
   def treeData5_1(): TreeNode = {
     val n1 = new TreeNode(1)
     val n2 = new TreeNode(2)