impl delete for BST

scala/src/main/scala/ch24_binary_search_tree/BinarySearchTree.scala

@@ -56,4 +56,76 @@ class BinarySearchTree(var root: Option[Node[Int]]) extends BinaryTree[Int] {
     }
     p
   }
+
+  def delete(data: Int): Unit = {
+    //there are 3 scenarios
+    //1: data is leaf node
+    //2: data has one child node
+    //3: data has two child nodes, we need to find out the smallest node from right branch
+    var p = root
+    var pp: Option[Node[Int]] = None //parent node of deleted node
+
+    //find matching node to delete
+    breakable {
+      while (p.isDefined) {
+        if (data > p.get.data) {
+          pp = p
+          p = p.get.right
+        } else if (data < p.get.data) {
+          pp = p
+          p = p.get.left
+        } else {
+          //find the value
+          break
+        }
+      }
+    }
+
+    if (p.isEmpty) {
+      //find nothing
+      return
+    }
+
+    //now we find the node to delete
+    //scenario 3
+    if (p.get.left.isDefined && p.get.right.isDefined) {
+      //need to find out the smallest node in right branch
+      var minPP = p
+      var minP = p.get.right
+      while (minP.get.left.isDefined) {
+        minPP = minP
+        minP = minP.get.left
+      }
+
+      //assign the smallest value in the right branch to the node to be deleted
+      p.get.data = minP.get.data
+      //now problems becomes delete the minP in the tree
+      //minP must not have any left child node
+      //minP may or may not have right child node
+      //it will fall back to scenario 1 or 2
+      p = minP
+      pp = minPP
+    }
+
+    //child is the child of p
+    var child: Option[Node[Int]] = None
+    if (p.get.left.isDefined) {
+      child = p.get.left
+    } else if (p.get.right.isDefined) {
+      child = p.get.right
+    }
+
+    //starting the node deletion
+    pp match {
+      case None => root = child
+      case Some(parentNode) => {
+        if (parentNode.left.isDefined && (parentNode.left.get.data == p.get.data)) {
+          parentNode.left = child
+        } else if (parentNode.right.isDefined && (parentNode.right.get.data == p.get.data)) {
+          parentNode.right = child
+        }
+      }
+    }
+
+  }
 }

scala/src/test/scala/ch24_binary_search_tree/BinarySearchTreeTest.scala

@@ -40,4 +40,16 @@ class BinarySearchTreeTest extends FlatSpec with Matchers {
     assert(tree.find(100).isEmpty)
   }
 
+  it should "delete" in {
+    val tree = new BinarySearchTree(None)
+    val nums = Array(33, 17, 50, 13, 18, 34, 58, 16, 25, 51, 66, 19, 27, 55)
+    nums.foreach(tree.insert)
+    tree.delete(13)
+    tree.inOrder(tree.root) should equal(nums.sorted.tail.mkString(""))
+    tree.delete(18)
+    tree.inOrder(tree.root) should equal("1617" + nums.sorted.slice(4, nums.size).mkString(""))
+    tree.delete(66)
+    tree.inOrder(tree.root) should equal("1617" + nums.sorted.slice(4, nums.size-1).mkString(""))
+  }
+
 }