add iterative dfs implementation

go-dsa/tree/bfs.go

@@ -1,6 +1,8 @@
 package tree
 
 func BFS(n *Node, f func(*Node)) {
+	// big o time complexity: O(n)
+	// big o space complexity: O(n)
 	if n == nil {
 		return
 	}

go-dsa/tree/dfs_in_order.go

@@ -9,3 +9,22 @@ func DFSInOrder(n *Node, f func(*Node)) {
 	f(n)
 	DFSInOrder(n.Right, f)
 }
+
+func DFSInOrderIterative(n *Node, f func(*Node)) {
+	// big O space: O(h) where h is the height of the tree
+	// big O time: O(n) where n is the number of nodes in the tree
+	var stack []*Node
+	current := n
+
+	for current != nil || len(stack) > 0 {
+		for current != nil {
+			stack = append(stack, current)
+			current = current.Left
+		}
+
+		current = stack[len(stack)-1]
+		stack = stack[:len(stack)-1]
+
+		current = current.Right
+	}
+}

go-dsa/tree/dfs_in_order_test.go

@@ -5,7 +5,7 @@ import (
 	"testing"
 )
 
-func TestDFSInOrder(t *testing.T) {
+func buildInOrderTree() *Node {
 	/*
 		Should print numbers in sequence: 1, 2, 3, 4, 5, 6
 			Tree:
@@ -23,7 +23,13 @@ func TestDFSInOrder(t *testing.T) {
 	root.Left.Right = NewNode(3)
 	root.Right.Right = NewNode(6)
 
+	return root
+}
+
+func TestDFSInOrder(t *testing.T) {
 	var result []int
+	root := buildInOrderTree()
+
 	DFSInOrder(root, func(n *Node) {
 		result = append(result, n.Value)
 	})
@@ -33,3 +39,17 @@ func TestDFSInOrder(t *testing.T) {
 		t.Errorf("Expected %v but got %v", expected, result)
 	}
 }
+
+func TestDFSInOrderIterative(t *testing.T) {
+	var result []int
+	root := buildInOrderTree()
+
+	expected := []int{1, 2, 3, 4, 5, 6}
+	DFSInOrderIterative(root, func(n *Node) {
+		result = append(result, n.Value)
+	})
+
+	if !reflect.DeepEqual(result, expected) {
+		t.Errorf("Expected %v but got %v", expected, result)
+	}
+}

go-dsa/tree/dfs_pre_order.go

@@ -9,3 +9,20 @@ func DFSPreOrder(n *Node, f func(*Node)) {
 	DFSPreOrder(n.Left, f)
 	DFSPreOrder(n.Right, f)
 }
+
+func DFSPreOrderIterative(n *Node, f func(*Node)) {
+	var stack []*Node
+	current := n
+
+	for current != nil || len(stack) > 0 {
+		for current != nil {
+			stack = append(stack, current)
+			current = current.Left
+		}
+
+		current = stack[len(stack)-1]
+		stack = stack[:len(stack)-1]
+
+		current = current.Right
+	}
+}

go-dsa/tree/dfs_pre_order_test.go

@@ -5,15 +5,14 @@ import (
 	"testing"
 )
 
-func TestDFSPreOrder(t *testing.T) {
+func buildPreOrderTree() *Node {
 	/*
-		Should print numbers in sequence: 1, 2, 3, 4, 5, 6
-			Tree:
-				1
-			   /  \
-			  2    5
-			 / \     \
-			3   4     6
+		Tree:
+			1
+		   /  \
+		  2    5
+		 / \     \
+		3   4     6
 	*/
 	root := NewNode(1)
 	root.Left = NewNode(2)
@@ -22,7 +21,13 @@ func TestDFSPreOrder(t *testing.T) {
 	root.Left.Right = NewNode(4)
 	root.Right.Right = NewNode(6)
 
+	return root
+}
+
+func TestDFSPreOrder(t *testing.T) {
 	var result []int
+	root := buildPreOrderTree()
+
 	DFSPreOrder(root, func(n *Node) {
 		result = append(result, n.Value)
 	})
@@ -32,3 +37,17 @@ func TestDFSPreOrder(t *testing.T) {
 		t.Errorf("Expected %v but got %v", expected, result)
 	}
 }
+
+func TestDFSPreOrderIterative(t *testing.T) {
+	var result []int
+	root := buildPreOrderTree()
+
+	expected := []int{1, 2, 3, 4, 5, 6}
+	DFSPreOrderIterative(root, func(n *Node) {
+		result = append(result, n.Value)
+	})
+
+	if !reflect.DeepEqual(result, expected) {
+		t.Errorf("Expected %v but got %v", expected, result)
+	}
+}