add reverse tree (#89)

Author: spring1843

README.md

@@ -26,7 +26,7 @@ Welcome to **Data Structures and Algorithms in Go**! 🎉 This project is design
         * [Equal Sum Sub-arrays](./array/equal_sum_subarrays_test.go)
         * [Rotate K Times](./array/rotate_k_steps_test.go)
         * [Bubble Sort](./array/bubble_sort_test.go)
-        * [Insertion Sort](./array/insertion_sort_test.go), [Solution](./array/insertion_sort.go)
+        * [Insertion Sort](./array/insertion_sort_test.go)
     * [Strings](./strings/README.md)
         * [The longest Dictionary Word Containing Key](./strings/longest_dictionary_word_test.go)
         * [Look and Tell](./strings/look_and_tell_test.go)
@@ -38,7 +38,7 @@ Welcome to **Data Structures and Algorithms in Go**! 🎉 This project is design
         * [Linked List Serialization](./linkedlist/serialization_test.go)
         * [Reverse a Linked List In-place](./linkedlist/reverse_in_place_test.go)
         * [Join Two Sorted Linked Lists](./linkedlist/join_sorted_lists_test.go)
-        * [Keep Repetitions](./linkedlist/keep_repetitions_test.go), [Solution](./linkedlist/keep_repetitions_test.go)
+        * [Keep Repetitions](./linkedlist/keep_repetitions_test.go)
         * [Copy Linked List with Random Pointer](./linkedlist/copy_linklist_with_random_pointer_test.go)
         * [Implement LRU Cache](./linkedlist/lru_cache_test.go)
     * [Stacks](./stack/README.md)
@@ -65,14 +65,15 @@ Welcome to **Data Structures and Algorithms in Go**! 🎉 This project is design
         * [Evaluate A Binary Expression Tree](./tree/evaluate_expression_test.go)
         * [Sorted Array to Balanced BST](./tree/sorted_array_to_balanced_bsd_test.go)
         * [Traverse Binary Tree](./tree/traverse_binary_tree_test.go)
+        * [Reverse Binary Tree](./tree/reverse_binary_tree_test.go)
         * [Implement Autocomplete](./tree/auto_complete_test.go)
     * [Heaps](./heap/README.md)
         * [Kth Largest Element](./heap/kth_largest_element_test.go)
         * [Merge Sorted Lists](./heap/merge_sorted_list_test.go)
         * [Median in a Stream](./heap/median_in_a_stream_test.go)
         * [Kth Closest Points to the Center](./heap/k_closest_points_to_origin_test.go)
         * [Sliding Maximum](./heap/sliding_maximum_test.go)
-        * [Heap Sort](./heap/heap_sort_test.go), [Solution](./heap/heap_sort.go)
+        * [Heap Sort](./heap/heap_sort_test.go)
 * Algorithms
     * [Recursion](./recursion/README.md)
         * [Reverse an integer recursively](./recursion/reverse_number_test.go)

heap/README.md

@@ -95,9 +95,9 @@ Priority queues implemented as heaps are utilized in job scheduling, for example
 
 ## Rehearsal
 
-* [Kth Largest Element](kth_largest_element_test.go), [Solution](kth_largest_element.go)
-* [Merge Sorted Lists](merge_sorted_list_test.go), [Solution](merge_sorted_list.go)
-* [Median in a Stream](median_in_a_stream_test.go), [Solution](median_in_a_stream_test.go)
-* [Kth Closest Points to the Center](k_closest_points_to_origin_test.go), [Solution](k_closest_points_to_origin.go)
-* [Sliding Maximum](sliding_maximum_test.go), [Solution](sliding_maximum.go)
-* [Heap Sort](heap_sort_test.go), [Solution](heap_search.go)
+* [Kth Largest Element](./kth_largest_element_test.go), [Solution](./kth_largest_element.go)
+* [Merge Sorted Lists](./merge_sorted_list_test.go), [Solution](./merge_sorted_list.go)
+* [Median in a Stream](./median_in_a_stream_test.go), [Solution](./median_in_a_stream_test.go)
+* [Kth Closest Points to the Center](./k_closest_points_to_origin_test.go), [Solution](./k_closest_points_to_origin.go)
+* [Sliding Maximum](./sliding_maximum_test.go), [Solution](./sliding_maximum.go)
+* [Heap Sort](./heap_sort_test.go), [Solution](./heap_sort.go)

tree/README.md

@@ -70,8 +70,9 @@ Trees, such as Binary Search Trees (BSTs), can offer a time complexity of O(Log
 
 ## Rehearsal
 
-* [Serialize Binary Tree](serialize_tree_test.go), [Solution](serialize_tree.go)
-* [Evaluate A Binary Expression Tree](evaluate_expression_test.go), [Solution](evaluate_expression.go)
-* [Sorted Array to Balanced BST](sorted_array_to_balanced_bsd_test.go), [Solution](sorted_array_to_balanced_bsd.go)
-* [Traverse Binary Tree](traverse_binary_tree_test.go), [Solution](traverse_binary_tree.go)
-* [Implement Autocomplete](auto_complete_test.go), [Solution](auto_complete.go)
+* [Serialize Binary Tree](./serialize_tree_test.go), [Solution](./serialize_tree.go)
+* [Evaluate A Binary Expression Tree](./evaluate_expression_test.go), [Solution](./evaluate_expression.go)
+* [Sorted Array to Balanced BST](./sorted_array_to_balanced_bsd_test.go), [Solution](./sorted_array_to_balanced_bsd.go)
+* [Traverse Binary Tree](./traverse_binary_tree_test.go), [Solution](./traverse_binary_tree.go)
+* [Reverse Binary Tree](./reverse_binary_tree_test.go), [Solution](./reverse_binary_tree_test.go)
+* [Implement Autocomplete](./auto_complete_test.go), [Solution](./auto_complete.go)

tree/reverse_binary_tree.go

@@ -0,0 +1,10 @@
+package tree
+
+// ReverseBinaryTree solves the problem in O(n) time and O(1) space.
+func ReverseBinaryTree(root *BinaryTreeNode) *BinaryTreeNode {
+	if root == nil {
+		return nil
+	}
+	root.Left, root.Right = ReverseBinaryTree(root.Right), ReverseBinaryTree(root.Left)
+	return root
+}

tree/reverse_binary_tree_test.go

@@ -0,0 +1,41 @@
+package tree
+
+import "testing"
+
+/*
+TestReverseBinaryTree tests solution(s) with the following signature and problem description:
+
+			func ReverseBinaryTree(root *BinaryTreeNode) *BinaryTreeNode
+
+
+	     1
+	   /   \
+	  2     3
+	 / \   / \
+	4   5 6   7
+
+Reverse a binary search tree, the above tree should become:
+
+	     1
+	   /   \
+	  3     2
+	 / \   / \
+	7   6 5   4
+*/
+func TestReverseBinaryTree(t *testing.T) {
+	tests := []struct {
+		tree, reversed string
+	}{
+		{"", ""},
+		{"1,2,3", "1,3,2"},
+		{"1,2,nil", "1,nil,2"},
+		{"1,2,3,4,5,6,7", "1,3,2,7,6,5,4"},
+		{"1,2,3,4", "1,3,2,nil,nil,nil,4"},
+	}
+
+	for i, test := range tests {
+		if got := Serialize(ReverseBinaryTree(Unserialize(test.tree))); got != test.reversed {
+			t.Fatalf("Failed test case #%d. Want %s got %s", i, test.reversed, got)
+		}
+	}
+}