236. Lowest Common Ancestor of a Binary Tree

README.md

@@ -115,6 +115,7 @@ continually updating 😃.
 * [208. Implement Trie (Prefix Tree)](src/0208_implement_trie_prefix_tree/impltrie.go)   *`trie`*
 * [226. Invert Binary Tree](src/0226_invert_binary_tree/invert_binary_tree.go)   *`binary tree`*
 * [235. Lowest Common Ancestor of a Binary Search Tree](src/0235_lowest_common_ancestor_of_a_binary_search_tree/lcaoabst.go)   *`binary tree`*
+* [236. Lowest Common Ancestor of a Binary Tree](src/0236_Lowest_Common_Ancestor_of_a_Binary_Tree/lca.go)   *`binary tree`*
 * [257. Binary Tree Paths](src/0257_binary_tree_paths/binary_tree_paths.go)   *`binary tree`*
 * [307. Range Sum Query - Mutable](src/0307_Range_Sum_Query_Mutable/range_sum_query_mut.go)   *`segment tree`*
 * [404. Sum of Left Leaves](src/0404_sum_of_left_leaves/sum_of_left_leaves.go)   *`binary tree`*

src/0236_Lowest_Common_Ancestor_of_a_Binary_Tree/lca.go

@@ -0,0 +1,30 @@
+/*
+236. Lowest Common Ancestor of a Binary Tree
+https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/
+*/
+// 2019-02-21
+
+package lca
+
+// TreeNode Definition for TreeNode.
+type TreeNode struct {
+	Val   int
+	Left  *TreeNode
+	Right *TreeNode
+}
+
+func lowestCommonAncestor(root, p, q *TreeNode) *TreeNode {
+	if root == nil || root == p || root == q {
+		return root
+	}
+	left := lowestCommonAncestor(root.Left, p, q)
+	right := lowestCommonAncestor(root.Right, p, q)
+
+	if left != nil && right != nil {
+		return root
+	}
+	if left != nil {
+		return left
+	}
+	return right
+}

src/0236_Lowest_Common_Ancestor_of_a_Binary_Tree/lca_test.go

@@ -0,0 +1,39 @@
+package lca
+
+import "testing"
+
+func TestLCA(t *testing.T) {
+	type arg struct {
+		root, p, q *TreeNode
+	}
+
+	tree := createBinaryTree([]int{6, 2, 8, 0, 4, 7, 9, -1, 1, 3, 5})
+
+	testCases := []arg{
+		{root: tree, p: tree.Left.Right.Left, q: tree.Left.Right.Right},
+		{p: &TreeNode{Val: 2}, q: &TreeNode{Val: 8}},
+	}
+	expected := []*TreeNode{{Val: 4}, nil}
+
+	for index, data := range testCases {
+		if res := lowestCommonAncestor(data.root, data.p, data.q); res != nil && res.Val != expected[index].Val {
+			t.Errorf("expected %v, got %v", expected[index], res)
+		} else if res == nil && res != expected[index] {
+			t.Errorf("expected %v, got %v", expected[index], res)
+		}
+	}
+}
+
+func createBinaryTree(nums []int) *TreeNode {
+	return performCreate(nums, 0)
+}
+
+func performCreate(nums []int, index int) *TreeNode {
+	if index >= len(nums) {
+		return nil
+	}
+	root := &TreeNode{Val: nums[index]}
+	root.Left = performCreate(nums, 2*index+1)
+	root.Right = performCreate(nums, 2*index+2)
+	return root
+}

src/README.md

@@ -76,6 +76,7 @@
 |0219|[219. Contains Duplicate II](0219_contains_duplicate_2/contains_duplicate_2.go)|Easy|*`map`*|
 |0226|[Invert Binary Tree](./0226_invert_binary_tree/invert_binary_tree.go)|Easy|*`recursion; `* *`binary tree`*|
 |0235|[235. Lowest Common Ancestor of a Binary Search Tree](0235_lowest_common_ancestor_of_a_binary_search_tree/lcaoabst.go)|Easy|*`recursion; `* *`binary tree`*|
+|0236|[236. Lowest Common Ancestor of a Binary Tree](0236_Lowest_Common_Ancestor_of_a_Binary_Tree/lca.go)|Medium|*`recursion; `* *`binary tree`*|
 |0237|[237. Delete Node in a Linked List](0237_delete_node_in_a_linked_list/dniall.go)|Easy|*`linked list`*|
 |0257|[257. Binary Tree Paths](0257_binary_tree_paths/binary_tree_paths.go)|Easy|*`binary tree`*|
 |0258|[258. Add Digits](0258_add_digits/add_digits.go)|Easy|*`math`*|