036

Author: TipsyPixie

README.md

@@ -14,8 +14,8 @@ make test # test all
 
 ## Problems
 
-Number | Difficulty | Asked By
---- | --- | --- |
+Number | Difficulty | Asked By | Title
+--- | --- | --- | --- |
 [#1](problem001) | EASY | Google
 [#2](problem002) | HARD | Uber
 [#3](problem003) | MEDIUM | Google
@@ -51,4 +51,4 @@ Number | Difficulty | Asked By
 [#33](problem033) | EASY | Microsoft
 [#34](problem034) | MEDIUM | Quora
 [#35](problem035) | HARD | Google
-
+[#36](problem036) | MEDIUM | Dropbox | Finding the second largest node in BST

problem036/README.md

@@ -0,0 +1,7 @@
+## Daily Coding Problem: Problem #36 [MEDIUM]
+
+Good morning! Here's your coding interview problem for today.
+
+This problem was asked by Dropbox.
+
+Given the root to a binary search tree, find the second largest node in the tree.

problem036/problem036.go

@@ -0,0 +1,44 @@
+package problem036
+
+type binarySearchTree struct {
+	value      int
+	leftChild  *binarySearchTree
+	rightChild *binarySearchTree
+}
+
+func NewBstNode(value int) *binarySearchTree {
+	return &binarySearchTree{
+		value:      value,
+		leftChild:  nil,
+		rightChild: nil,
+	}
+}
+
+func (root *binarySearchTree) Insert(value int) *binarySearchTree {
+	tree := root
+	for {
+		if value > tree.value {
+			if tree.rightChild == nil {
+				tree.rightChild = NewBstNode(value)
+				return root
+			}
+			tree = tree.rightChild
+		} else {
+			if tree.leftChild == nil {
+				tree.leftChild = NewBstNode(value)
+				return root
+			}
+			tree = tree.leftChild
+		}
+	}
+}
+
+func (root *binarySearchTree) FindSecondLargest() *binarySearchTree {
+	var parentTree *binarySearchTree
+	tree := root
+	for tree.rightChild != nil {
+		parentTree = tree
+		tree = tree.rightChild
+	}
+	return parentTree
+}

problem036/problem036_test.go

@@ -0,0 +1,19 @@
+package problem036
+
+import "testing"
+
+func TestBinarySearchTree_FindSecondLargest(t *testing.T) {
+	tree := NewBstNode(10).Insert(7).Insert(5).Insert(14).Insert(9)
+	result := tree.FindSecondLargest().value
+	if result != 10 {
+		t.Fail()
+		t.Log(result)
+	}
+
+	tree = NewBstNode(1).Insert(2).Insert(5).Insert(4).Insert(3).Insert(11)
+	result = tree.FindSecondLargest().value
+	if result != 5 {
+		t.Fail()
+		t.Log(result)
+	}
+}