add scala #337

scala-leetcode/src/main/scala/io/github/dreamylost/Leetcode_337_Tree.scala

@@ -18,15 +18,69 @@ package io.github.dreamylost
   * @time 2018年8月10日
   * @version v1.0
   */
-object Leetcode_337_Tree extends App {
+object Leetcode_337_Tree {
 
+  /**
+    * 对于一个以 root 为根节点的二叉树而言，如果尝试偷取 root 节点，那么势必不能偷取其左右子节点，然后继续尝试偷取其左右子节点的左右子节点。
+    * 如果不偷取该节点，那么只能尝试偷取其左右子节点比较两种方式的结果，谁大取谁。
+    *
+    * 3768 ms,8.33%
+    * fold 4848ms
+    * 54.9 MB,100.00%
+    *
+    * @param root
+    * @return
+    */
   def rob(root: TreeNode): Int = {
+    if (root == null) return 0
+    val memory = new scala.collection.mutable.HashMap[TreeNode, Int]()
+    if (memory.contains(root)) return memory(root)
+    var ccVal = root.value
+    if (root.left != null) ccVal += rob(root.left.left) + rob(root.left.right)
+    if (root.right != null) ccVal += rob(root.right.left) + rob(root.right.right)
+    val cVal = rob(root.left) + rob(root.right)
+    memory.put(root, ccVal)
+    math.max(cVal, ccVal)
+  }
+
+  /**
+    * 解决重复子问题，竟然还慢
+    *
+    * 1372 ms,33.33%
+    * 52.2 MB,100.00%
+    *
+    * @param root
+    * @return
+    */
+  def rob_(root: TreeNode): Int = {
     if (root == null) return 0
     var vart = root.value
-    if (root.left != null) vart += rob(root.left.left) + rob(root.right.right)
-    if (root.right != null) vart += rob(root.right.right) + rob(root.right.right)
-    var valt = rob(root.left) + rob(root.right)
+    if (root.left != null) vart += rob(root.left.left) + rob(root.left.right)
+    if (root.right != null) vart += rob(root.right.left) + rob(root.right.right)
+    val valt = rob(root.left) + rob(root.right)
     math.max(valt, vart)
   }
 
+  /**
+    * 后续中递归
+    *
+    * 688 ms,100.00%
+    * 53.1 MB,100.00%
+    *
+    * @param root
+    * @return
+    */
+  def rob2(root: TreeNode): Int = {
+    if (root == null) return 0
+    def helper(r: TreeNode): Seq[Int] = {
+      if (r == null) return Seq(0, 0)
+      // index 0 存储 下下层，偷root和root的下下层节点
+      // index 1 存储下层（即不偷当前子树的root，而是偷root的左右子节点）
+      val left = helper(r.left)
+      val right = helper(r.right)
+      val h = math.max(left.head + right.head + r.value, left(1) + right(1))
+      Seq(left(1) + right(1), h)
+    }
+    helper(root)(1)
+  }
 }

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

@@ -17,7 +17,7 @@
 * [统计左叶子节点的和](./Leetcode_404_Tree.scala)
 * [最小路径](./Leetcode_111_Tree.scala)
 * [判断路径和是否等于一个数](./Leetcode_112_Tree.scala)
-* [间隔遍历](./Leetcode_337_Tree.scala)
+* [间隔遍历/打家劫舍 III](./Leetcode_337_Tree.scala)
 * [两节点的最长路径](./Leetcode_543_Tree.scala)
 * [路径总和 III](./Leetcode_437_Tree.scala)
 * [二叉搜索树中的众数](./Leetcode_501.scala)