Symmetric Tree

Author: ignacio-chiazzo

LeetcodeProblems/Symmetric_Tree.js

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+/*
+Symmetric Tree
+
+https://leetcode.com/problems/symmetric-tree/description/
+
+Given a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).
+
+For example, this binary tree [1,2,2,3,4,4,3] is symmetric:
+
+    1
+   / \
+  2   2
+ / \ / \
+3  4 4  3
+But the following [1,2,2,null,3,null,3] is not:
+    1
+   / \
+  2   2
+   \   \
+   3    3
+Note:
+Bonus points if you could solve it both recursively and iteratively.
+*/
+
+/**
+ * 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 === null)
+        return true; 
+    return isSymetricAux(root.left, root.right);
+};
+
+var isSymetricAux = function(root1, root2) {
+    if(root1 === null)
+        return root2 === null;
+    
+    if(root2 === null || root1.val !== root2.val) {
+        return false;
+    }
+    
+    return isSymetricAux(root1.left, root2.right) && isSymetricAux(root1.right, root2.left);
+}