Add week 7 solutions : lowestCommonAncestorOfABinarySearchTree

Author: yolophg

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

@@ -0,0 +1,26 @@
+// Time Complexity: O(n)
+// Space Complexity: O(1)
+
+var lowestCommonAncestor = function (root, p, q) {
+  // start from the root.
+  let current = root;
+
+  // traverse the tree.
+  while (current !== null) {
+    // if both p and q are greater than current node, LCA lies in the right.
+    if (p.val > current.val && q.val > current.val) {
+      current = current.right;
+    }
+    // if both p and q are smaller than current node, LCA lies in the left.
+    else if (p.val < current.val && q.val < current.val) {
+      current = current.left;
+    }
+    // if one of p or q is on one side and the other is on the other side, It's LCA.
+    else {
+      return current;
+    }
+  }
+
+  // if the tree is empty.
+  return null;
+};