binary search tree O(n) O(n)

Author: lukeist

leetcode-108-convertSortedArrayToBinarySearchTree.js

@@ -1,41 +1,53 @@
-/**
- * Definition for a binary tree node.
- * function TreeNode(val, left, right) {
- *     this.val = (val===undefined ? 0 : val)
- *     this.left = (left===undefined ? null : left)
- *     this.right = (right===undefined ? null : right)
- * }
- */
-/**
- * @param {number[]} nums
- * @return {TreeNode}
- */
-// p: array
-// r: bi search tree
-//   0       3 4
-//         j
-//   i   j   r
-//   i   j   i j
-// [-10,-3,0,5,9] Math.floor(i+j/2 = 2.5) = 2 => root
-//  0     3
-// [1,3,4,6] => root i
-//j r ij
-// [1,3] root = 1
-
 var sortedArrayToBST = function (nums, i = 0, j = nums.length - 1) {
   if (i > j) return null;
-  const rootIndex = Math.floor((i + j) / 2);
-  const root = new TreeNode(nums[rootIndex]);
-  root.left = sortedArrayToBST(nums, i, rootIndex - 1);
-  root.right = sortedArrayToBST(nums, rootIndex + 1, j);
+  const mid = Math.floor((i + j) / 2);
+  const rootVal = nums[mid];
+  const root = new TreeNode(rootVal);
+
+  root.left = sortedArrayToBST(nums, i, mid - 1);
+  root.right = sortedArrayToBST(nums, mid + 1, j);
+
   return root;
 };
 
-// var sortedArrayToBST = function(nums) {
-//     if (nums.length === 0) return null;
-//     const rootIndex = Math.floor(nums.length / 2)
-//     const root = new TreeNode(nums[rootIndex]);
-//     root.left = sortedArrayToBST(nums.slice(0, rootIndex));
-//     root.right = sortedArrayToBST(nums.slice(rootIndex + 1));
-//     return root;
+// /**
+//  * Definition for a binary tree node.
+//  * function TreeNode(val, left, right) {
+//  *     this.val = (val===undefined ? 0 : val)
+//  *     this.left = (left===undefined ? null : left)
+//  *     this.right = (right===undefined ? null : right)
+//  * }
+//  */
+// /**
+//  * @param {number[]} nums
+//  * @return {TreeNode}
+//  */
+// // p: array
+// // r: bi search tree
+// //   0       3 4
+// //         j
+// //   i   j   r
+// //   i   j   i j
+// // [-10,-3,0,5,9] Math.floor(i+j/2 = 2.5) = 2 => root
+// //  0     3
+// // [1,3,4,6] => root i
+// //j r ij
+// // [1,3] root = 1
+
+// var sortedArrayToBST = function (nums, i = 0, j = nums.length - 1) {
+//   if (i > j) return null;
+//   const rootIndex = Math.floor((i + j) / 2);
+//   const root = new TreeNode(nums[rootIndex]);
+//   root.left = sortedArrayToBST(nums, i, rootIndex - 1);
+//   root.right = sortedArrayToBST(nums, rootIndex + 1, j);
+//   return root;
 // };
+
+// // var sortedArrayToBST = function(nums) {
+// //     if (nums.length === 0) return null;
+// //     const rootIndex = Math.floor(nums.length / 2)
+// //     const root = new TreeNode(nums[rootIndex]);
+// //     root.left = sortedArrayToBST(nums.slice(0, rootIndex));
+// //     root.right = sortedArrayToBST(nums.slice(rootIndex + 1));
+// //     return root;
+// // };