Improve debug output for binary search tree

Author: hollance

Binary Search Tree/README.markdown

@@ -226,15 +226,13 @@ When working with somewhat complicated data structures such as this, it's useful
 ```swift
 extension BinarySearchTree: CustomStringConvertible {
   public var description: String {
-    var s = "value: \(value)"
-    if let parent = parent {
-      s += ", parent: \(parent.value)"
-    }
+    var s = ""
     if let left = left {
-      s += ", left = [" + left.description + "]"
+      s += "(\(left.description)) <- "
     }
+    s += "\(value)"
     if let right = right {
-      s += ", right = [" + right.description + "]"
+      s += " -> (\(right.description))"
     }
     return s
   }
@@ -243,16 +241,7 @@ extension BinarySearchTree: CustomStringConvertible {
 
 When you do a `print(tree)`, you should get something like this:
 
-	value: 7, left = [value: 2, parent: 7, left = [value: 1, parent: 2], right = [value: 5, parent: 2]], right = [value: 10, parent: 7, left = [value: 9, parent: 10]]
-
-To make this a bit clearer to understand, reformat it slightly:
-
-	value: 7, 
-		left = [value: 2, parent: 7, 
-			left = [value: 1, parent: 2], 
-			right = [value: 5, parent: 2]], 
-		right = [value: 10, parent: 7, 
-			left = [value: 9, parent: 10]]
+	((1) <- 2 -> (5)) <- 7 -> ((9) <- 10)
 
 With some imagination, you should see now that this indeed corresponds to the following tree:
 
@@ -477,17 +466,19 @@ Try it out:
 
 ```swift
 if let node2 = tree.search(2) {
+  print(tree)     // before
   node2.remove()
+  print(tree)     // after
 }
 ```
 
-First you find the node that you want to remove with `search()` and then you call `remove()` on that object. If you now print out the tree you get:
+First you find the node that you want to remove with `search()` and then you call `remove()` on that object. Before the removal, the tree printed like this:
+
+	((1) <- 2 -> (5)) <- 7 -> ((9) <- 10)
+
+But after `remove()` you get:
 
-	value: 7, 
-		left = [value: 5, parent: 7, 
-			left = [value: 1, parent: 5]], 
-		right = [value: 10, parent: 7, 
-			left = [value: 9, parent: 10]]
+	((1) <- 5) <- 7 -> ((9) <- 10)
 
 As you can see, node `5` has taken the place of `2`. In fact, if you do `print(node2)` you'll see that it now has the value `5`. We didn't actually remove the `node2` object, we just gave it a new value.
 

Binary Search Tree/Solution 1/BinarySearchTree.playground/Contents.swift

@@ -6,7 +6,9 @@ tree.insert(5)
 tree.insert(10)
 tree.insert(9)
 tree.insert(1)
+
 tree
+tree.debugDescription
 
 let tree2 = BinarySearchTree<Int>(array: [7, 2, 5, 10, 9, 1])
 
@@ -24,7 +26,7 @@ tree.maximum()
 
 if let node2 = tree.search(2) {
   node2.remove()
-  node2            // this is now node "5"
+  node2.value          // this is now node "5"
   print(tree)
 }
 

Binary Search Tree/Solution 1/BinarySearchTree.playground/Sources/BinarySearchTree.swift

@@ -311,15 +311,29 @@ extension BinarySearchTree {
 
 extension BinarySearchTree: CustomStringConvertible {
   public var description: String {
+    var s = ""
+    if let left = left {
+      s += "(\(left.description)) <- "
+    }
+    s += "\(value)"
+    if let right = right {
+      s += " -> (\(right.description))"
+    }
+    return s
+  }
+}
+
+extension BinarySearchTree: CustomDebugStringConvertible {
+  public var debugDescription: String {
     var s = "value: \(value)"
     if let parent = parent {
       s += ", parent: \(parent.value)"
     }
     if let left = left {
-      s += ", left = [" + left.description + "]"
+      s += ", left = [" + left.debugDescription + "]"
     }
     if let right = right {
-      s += ", right = [" + right.description + "]"
+      s += ", right = [" + right.debugDescription + "]"
     }
     return s
   }

Binary Search Tree/Solution 1/BinarySearchTree.swift

@@ -311,15 +311,29 @@ extension BinarySearchTree {
 
 extension BinarySearchTree: CustomStringConvertible {
   public var description: String {
+    var s = ""
+    if let left = left {
+      s += "(\(left.description)) <- "
+    }
+    s += "\(value)"
+    if let right = right {
+      s += " -> (\(right.description))"
+    }
+    return s
+  }
+}
+
+extension BinarySearchTree: CustomDebugStringConvertible {
+  public var debugDescription: String {
     var s = "value: \(value)"
     if let parent = parent {
       s += ", parent: \(parent.value)"
     }
     if let left = left {
-      s += ", left = [" + left.description + "]"
+      s += ", left = [" + left.debugDescription + "]"
     }
     if let right = right {
-      s += ", right = [" + right.description + "]"
+      s += ", right = [" + right.debugDescription + "]"
     }
     return s
   }