Add details to tree problems (#179)

Author: spring1843

queue/symmetrical_binary_tree_test.go

@@ -42,7 +42,7 @@ func TestIsTreeSymmetrical(t *testing.T) {
 		{"2,4,4,5,6,6,5", true},
 	}
 	for i, test := range tests {
-		got, err := IsTreeSymmetrical(tree.Unserialize(test.tree))
+		got, err := IsTreeSymmetrical(tree.Deserialize(test.tree))
 		if err != nil {
 			t.Fatalf("Failed test case #%d. Unexpected error %s", i, err)
 		}

tree/README.md

@@ -15,7 +15,7 @@ Traversing a tree means exploring every node in a tree and performing some work
 1   3 5   7
 ```
 
-Tree traversal methods are named after the order in which the nodes are explored. For example, in Pre-Order traversal, the node is explored before its children; in Post-Order traversal, the node is explored after its children.
+Tree traversal methods are named after the order in which the nodes are explored. For example, in Pre-Order traversal, the node is explored before its children; in Post-Order traversal, the node is explored after its children. Children are always traversed from left to right.
 
 There are many types of trees. Some important tree types include:
 
@@ -29,7 +29,7 @@ There are many types of trees. Some important tree types include:
      1		 4	    1        * 	  1 - Is it a binary tree?
     /|\		/ \	   /        / \	    2 - Is it a complete binary tree?
    / | \       /   \	  2        /   \      3 - Is it a full binary tree?
-  2  5  6     2     6	 / \	  *     +
+  2  5  6     2     6	 / \	  *     +         1 2 3
  / \   / \     \   /	3   4    / \   / \	A 0 0 0
 3   4 7   8  	3 5	    	5   5 2   2	B 1 0 0
 						C 1 1 0
@@ -48,7 +48,7 @@ The time complexity of operations such as Search, Deletion, Insertion, and findi
 
 ## AVL - Height Balanced BST
 
-A height-balanced binary search tree has a height of O(Log n), and its left and right subtrees of all nodes have equal heights.
+An AVL tree is a height-balanced binary search tree has a height of O(Log n), and its left and right subtrees of all nodes have equal heights. AVL stands for the name of the people who came up with the idea.
 
 To maintain balance after an insertion, a single rotation is needed if the insertion is on the outer side, either left-left or right-right, while a double rotation is required if the insertion is on the inner side, either left-right or right-left.
 
@@ -66,7 +66,7 @@ Insertion and Search are done in O(K), where K is the length word length.
 
 ## Application
 
-Trees, such as Binary Search Trees (BSTs), offer O(Log n) time complexity for searches, which is superior to [linked lists](../linkedlist/)' and [array](../array/)'s linear access time. Trees are widely employed in search systems, and operating systems can represent file information using tree structures.
+Trees, such as Binary Search Trees (BSTs), offer O(Log n) time complexity for searches, which is superior to [linked lists](../linkedlist/)' and [array](../array/)'s linear access time. Trees are widely employed in search systems. Operating systems can represent file information using tree structures.
 
 ## Rehearsal
 

tree/autocompletion_test.go

@@ -10,9 +10,11 @@ TestAutocompletion tests solution(s) with the following signature and problem de
 
 	func (t *trie) AutoComplete(word string) []string
 
-Given a word like "car" and a dictionary like {"car","caravan","card","carpet","cap","ca"},
-return autocomplete suggestions where the given word is the prefix of a dictionary word
-like {"avan","d","pet"}.
+Given a dictionary of words and a word, return autocomplete suggestions from the dictionary that
+start with the given word.
+
+For example given {"car","caravan","card","carpet","cap","ca"}, and the word "car", return
+{"avan","d","pet"} because they are all words that start with "car".
 */
 func TestAutocompletion(t *testing.T) {
 	tests := []struct {
@@ -32,6 +34,7 @@ func TestAutocompletion(t *testing.T) {
 		{"ab", []string{"abc", "abcc", "abccd", "abd", "abe"}, []string{"c", "cc", "ccd", "d", "e"}},
 		{"ab", []string{"abc", "abcc", "abcd", "abd", "abe"}, []string{"c", "cc", "cd", "d", "e"}},
 		{"ab", []string{"abc", "abcd", "abd", "abcc", "abe"}, []string{"c", "cc", "cd", "d", "e"}},
+		{"car", []string{"car", "caravan", "card", "carpet", "cap", "ca"}, []string{"avan", "d", "pet"}},
 	}
 
 	for i, test := range tests {

tree/evaluate_expression_test.go

@@ -10,8 +10,17 @@ TestEvaluateBinaryExpressionTree tests solution(s) with the following signature
 
 	func EvaluateBinaryExpressionTree(node *stringBinaryTreeNode) (float64, error)
 
-Given an expression binary tree like (D) in _Figure2_ evaluate it to a float64 like 100 allowing four
-arithmetic operations.
+Given an expression binary tree that contains integers and the four basic arithmetic operations, return
+the resulting evaluation of the expression.
+
+		   *
+		  / \
+		 /   \
+		*     +
+	   / \   / \
+	  5   5 2   2
+
+For example given "*,*,+,5,5,2,2" representing the above tree return 100 because (5 * 5) * (2 + 2) = 100.
 */
 func TestEvaluateBinaryExpressionTree(t *testing.T) {
 	tests := []struct {

tree/reverse_binary_tree_test.go

@@ -5,22 +5,25 @@ import "testing"
 /*
 TestReverseBinaryTree tests solution(s) with the following signature and problem description:
 
-			func ReverseBinaryTree(root *BinaryTreeNode) *BinaryTreeNode
+	func ReverseBinaryTree(root *BinaryTreeNode) *BinaryTreeNode
 
+Given a binary tree, reverse it.
 
 	     1
 	   /   \
 	  2     3
 	 / \   / \
 	4   5 6   7
 
-Reverse a binary search tree, the above tree should become:
+For example given the above tree, return:
 
 	     1
 	   /   \
 	  3     2
 	 / \   / \
 	7   6 5   4
+
+Each tree is represented as a string by "1,2,3,4,5,6,7" and "1,3,2,7,6,5,4" respectively.
 */
 func TestReverseBinaryTree(t *testing.T) {
 	tests := []struct {
@@ -34,7 +37,7 @@ func TestReverseBinaryTree(t *testing.T) {
 	}
 
 	for i, test := range tests {
-		if got := Serialize(ReverseBinaryTree(Unserialize(test.tree))); got != test.reversed {
+		if got := Serialize(ReverseBinaryTree(Deserialize(test.tree))); got != test.reversed {
 			t.Fatalf("Failed test case #%d. Want %s got %s", i, test.reversed, got)
 		}
 	}

tree/serialize_tree.go

@@ -54,8 +54,8 @@ func Serialize(root *BinaryTreeNode) string {
 	return result
 }
 
-// Unserialize unserializes a given string into a binary tree in O(n) time and O(n) space.
-func Unserialize(s string) *BinaryTreeNode {
+// Deserialize a string into a binary tree in O(n) time and O(n) space.
+func Deserialize(s string) *BinaryTreeNode {
 	if s == "" {
 		return nil
 	}

tree/serialize_tree_test.go

@@ -5,8 +5,14 @@ import "testing"
 /*
 TestSerializeAndUnserializeBinaryTree tests solution(s) with the following signature and problem description:
 
+			type BinaryTreeNode struct {
+				Val int
+				Left *BinaryTreeNode
+				Right *BinaryTreeNode
+			}
+
 			func Serialize(root *BinaryTreeNode) string
-			func Unserialize(s string) *BinaryTreeNode
+			func Deserialize(s string) *BinaryTreeNode
 
 
 	     4
@@ -16,8 +22,11 @@ TestSerializeAndUnserializeBinaryTree tests solution(s) with the following signa
 	 / \   / \
 	    3 5
 
-Write two functions to serialize and unserialize a binary tree like the one above to and
-from a string like `4,2,6,nil,3,5,nil`.
+Given a binary tree, write a serialize and deserialize function that turns it into a string representation
+and back.
+
+For example given `4,2,6,nil,3,5,nil` representing the above tree, deserialize it to a *BinaryTreeNode,
+and given the *BinaryTreeNode serialize it back to `4,2,6,nil,3,5,nil`.
 */
 func TestSerializeAndUnserializeBinaryTree(t *testing.T) {
 	tests := []string{
@@ -29,7 +38,7 @@ func TestSerializeAndUnserializeBinaryTree(t *testing.T) {
 		"1,2,nil,4,nil,5,6",
 	}
 	for i, test := range tests {
-		if got := Serialize(Unserialize(test)); got != test {
+		if got := Serialize(Deserialize(test)); got != test {
 			t.Fatalf("Failed test case #%d. Want %#v got %#v", i, test, got)
 		}
 	}

tree/sorted_array_to_balanced_bsd_test.go

@@ -5,9 +5,23 @@ import "testing"
 /*
 TestBalancedBinarySearchTree tests solution(s) with the following signature and problem description:
 
+	type BinaryTreeNode struct {
+		Val int
+		Left *BinaryTreeNode
+		Right *BinaryTreeNode
+	}
 	func BalancedBinarySearchTree(sorted []int) *BinaryTreeNode
 
-Given a sorted array of integers like {1,2,3,4,5} return the root to a balanced BST.
+Given a sorted slice of integers like return a string representing the integers as a Balanced Binary Tree (BST).
+
+	     3
+	    / \
+	   /   \
+	  2     4
+	 /       \
+	1         5
+
+For example given return a *BinaryTreeNode that is the root element of the above tree.
 */
 func TestBalancedBinarySearchTree(t *testing.T) {
 	tests := []struct {

tree/traverse_binary_tree_test.go

@@ -10,15 +10,20 @@ TestTraverseBinaryTree tests solution(s) with the following signature and proble
 
 	func TraverseBinaryTree(root *BinaryTreeNode) ([]int, []int, []int)
 
+Given a binary tree like the above return the tree in-order, pre-order, and post-order traversals.
+
 	     4
 	    / \
 	   /   \
 	  2     6
 	 / \   / \
 	1   3 5   7
 
-Given a binary tree like the above one create three functions to traverse the
-tree in-order, pre-order, and post-order.
+For example given the above tree as "4,2,6,1,3,5,7" return:
+
+	in-order traversal as [1,2,3,4,5,6,7],
+	pre-order traversal as [4,2,1,3,6,5,7],
+	post-order traversal as [1,3,2,5,7,6,4].
 */
 func TestTraverseBinaryTree(t *testing.T) {
 	tests := []struct {
@@ -32,7 +37,7 @@ func TestTraverseBinaryTree(t *testing.T) {
 		{"4,2,6,nil,3,5", []int{2, 3, 4, 5, 6}, []int{4, 2, 3, 6, 5}, []int{3, 2, 5, 6, 4}},
 	}
 	for i, test := range tests {
-		gotIn, gotPre, gotPost := TraverseBinaryTree(Unserialize(test.tree))
+		gotIn, gotPre, gotPost := TraverseBinaryTree(Deserialize(test.tree))
 		if !slices.Equal(gotIn, test.in) {
 			t.Fatalf("Failed in-order test case #%d.  Want %#v got %#v", i, test.in, gotIn)
 		}