add JS Solution for 0101 0102 0108

Author: limbowandering

solution/0101.Symmetric Tree/Solution.js

@@ -0,0 +1,22 @@
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val) {
+ *     this.val = val;
+ *     this.left = this.right = null;
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @return {boolean}
+ */
+var isSymmetric = function(root) {
+  if (!root) return true
+  return checkSymmetric(root.left, root.right)  
+};
+
+const checkSymmetric = function(leftNode, rightNode) {
+  if (!leftNode && !rightNode) return true
+  if (!leftNode || !rightNode) return false
+  return leftNode.val === rightNode.val && checkSymmetric(leftNode.left, rightNode.right)
+    && checkSymmetric(rightNode.left, leftNode.right)
+}

solution/0102.Binary Tree Level Order Traversal/Solution.js

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+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val) {
+ *     this.val = val;
+ *     this.left = this.right = null;
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @return {number[][]}
+ */
+var levelOrder = function(root) {
+  let result = []
+  if (!root) return result
+
+  let queue = []
+  queue.push(root)
+  while(queue.length) {
+    let size = queue.length
+    let levelItems = []
+    while(size--) {
+      let node = queue.shift()
+      levelItems.push(node.val)
+      if(node.left) {
+        queue.push(node.left)
+      }
+      if(node.right) {
+        queue.push(node.right)
+      }
+    }
+    result.push(levelItems)
+  }
+  return result
+};

solution/0108.Convert Sorted Array to Binary Search Tree/Solution.js

@@ -0,0 +1,23 @@
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val) {
+ *     this.val = val;
+ *     this.left = this.right = null;
+ * }
+ */
+/**
+ * @param {number[]} nums
+ * @return {TreeNode}
+ */
+var sortedArrayToBST = function(nums) {
+  return nums ? buildTree(nums, 0, nums.length - 1) : null
+};
+
+const buildTree = function(nums, left, right) {
+  if (left > right) return null
+  let mid = Math.floor((left + right) / 2)
+  let root = new TreeNode(nums[mid])
+  root.left = buildTree(nums, left, mid - 1)
+  root.right = buildTree(nums, mid + 1, right)
+  return root
+}