refactor: Lowest Common Ancestor of a Binary Search Tree

Author: gwbaik9717

lowest-common-ancestor-of-a-binary-search-tree/gwbaik9717.js

@@ -1,5 +1,6 @@
-// Time complexity: O(logn)
-// Space complexity: O(logn)
+// h : height of BST
+// Time complexity: O(h)
+// Space complexity: O(h)
 
 /**
  * Definition for a binary tree node.
@@ -16,41 +17,13 @@
  * @return {TreeNode}
  */
 var lowestCommonAncestor = function (root, p, q) {
-  // 1. 각자 부모 리스트 완성
-  const search = (target, parent) => {
-    const dfs = (current) => {
-      if (target.val > current.val) {
-        dfs(current.right);
-      }
-
-      if (target.val < current.val) {
-        dfs(current.left);
-      }
-
-      parent.push(current);
-    };
-
-    dfs(root);
-  };
-
-  const parentP = [];
-  const parentQ = [];
-
-  search(p, parentP);
-  search(q, parentQ);
-
-  // 2. 공통 부모 탐색
-  let answer = null;
+  if (root.val < p.val && root.val < q.val && root.left) {
+    return lowestCommonAncestor(root.right, p, q);
+  }
 
-  while (
-    parentP.at(-1) &&
-    parentQ.at(-1) &&
-    parentP.at(-1).val === parentQ.at(-1).val
-  ) {
-    answer = parentP.at(-1);
-    parentP.pop();
-    parentQ.pop();
+  if (root.val > p.val && root.val > q.val && root.right) {
+    return lowestCommonAncestor(root.left, p, q);
   }
 
-  return answer;
+  return root;
 };