197th Commit

README.md

@@ -176,13 +176,14 @@ Ace Coding Interview with 75 Qs
 | 1448. Count Good Nodes in Binary Tree        | [Solution][1448] | Medium |
 | 437. Path Sum III                            | [Solution][437]  | Medium |
 | 1372. Longest ZigZag Path in a Binary Tree   | [Solution][1372] | Medium |
-| 236. Lowest Common Ancestor of a Binary Tree | Solution         | Medium |
+| 236. Lowest Common Ancestor of a Binary Tree | [Solution][236]  | Medium |
 
 [104]: ./src/page-2/104.%20Maximum%20Depth%20of%20Binary%20Tree/maxDepth.ts
 [872]: ./src/page-9/872.%20Leaf-Similar%20Trees/leafSimilar.ts
 [1448]: ./src/page-14/1448.%20Count%20Good%20Nodes%20in%20Binary%20Tree/goodNodes.ts
 [437]: ./src/page-5/437.%20Path%20Sum%20III/pathSum.ts
 [1372]: ./src/page-13/1372.%20Longest%20ZigZag%20Path%20in%20a%20Binary%20Tree/longestZigZag.ts
+[236]: ./src/page-3/236.%20Lowest%20Common%20Ancestor%20of%20a%20Binary%20Tree/lowestCommonAncestor.ts
 
 | Binary Tree - BFS                        |          |        |
 | ---------------------------------------- | -------- | ------ |

src/page-3/236. Lowest Common Ancestor of a Binary Tree/lowestCommonAncestor.test.ts

@@ -0,0 +1,45 @@
+import { TreeNode } from '~/utils/binary-tree';
+
+import { lowestCommonAncestor } from './lowestCommonAncestor';
+
+describe('236. Lowest Common Ancestor of a Binary Tree', () => {
+  test('lowestCommonAncestor', () => {
+    {
+      const node6 = new TreeNode(6);
+      const node7 = new TreeNode(7);
+      const node4 = new TreeNode(4);
+      const node2 = new TreeNode(2, node7, node4);
+      const node0 = new TreeNode(0);
+      const node8 = new TreeNode(8);
+      const node5 = new TreeNode(5, node6, node2);
+      const node1 = new TreeNode(1, node0, node8);
+      const root = new TreeNode(3, node5, node1);
+      const p = node5;
+      const q = node1;
+      expect(lowestCommonAncestor(root, p, q)?.val).toBe(3);
+    }
+
+    {
+      const node6 = new TreeNode(6);
+      const node7 = new TreeNode(7);
+      const node4 = new TreeNode(4);
+      const node2 = new TreeNode(2, node7, node4);
+      const node0 = new TreeNode(0);
+      const node8 = new TreeNode(8);
+      const node5 = new TreeNode(5, node6, node2);
+      const node1 = new TreeNode(1, node0, node8);
+      const root = new TreeNode(3, node5, node1);
+      const p = node5;
+      const q = node4;
+      expect(lowestCommonAncestor(root, p, q)?.val).toBe(5);
+    }
+
+    {
+      const node2 = new TreeNode(2);
+      const root = new TreeNode(1, node2, null);
+      const p = root;
+      const q = node2;
+      expect(lowestCommonAncestor(root, p, q)?.val).toBe(1);
+    }
+  });
+});

src/page-3/236. Lowest Common Ancestor of a Binary Tree/lowestCommonAncestor.ts

@@ -0,0 +1,26 @@
+import type { TreeNode } from '~/utils/binary-tree';
+
+type LowestCommonAncestor = (
+  root: TreeNode | null,
+  p: TreeNode | null,
+  q: TreeNode | null,
+) => TreeNode | null;
+
+/**
+ * Accepted
+ */
+export const lowestCommonAncestor: LowestCommonAncestor = (root, p, q) => {
+  if (root === null || root === p || root === q) return root;
+
+  // Perform DFS on the left subtree
+  const left = lowestCommonAncestor(root.left, p, q);
+
+  // Perform DFS on the right subtree
+  const right = lowestCommonAncestor(root.right, p, q);
+
+  // If both left and right are non-null, the current node is the LCA
+  if (left !== null && right !== null) return root;
+
+  // If only one of the sides is non-null, return that side
+  return left !== null ? left : right;
+};