removed redundant checks

AlveeM · AlveeM · commit c0ccab7654ac · 2021-07-16T10:37:30.000-04:00
diff --git a/leetcode/learn-cards/binary-tree/06_symmetric_tree.py b/leetcode/learn-cards/binary-tree/06_symmetric_tree.py
@@ -1,3 +1,38 @@
+# recursive
 class Solution:
-    def isSymmetric(self, root):
-        pass
+    def isSymmetric(self, root: TreeNode) -> bool:
+        if not root: return True
+        return self.isMirror(root.left, root.right)
+        
+    def isMirror(self, nodeLeft, nodeRight):
+        if not nodeLeft and not nodeRight: return True
+        if not nodeLeft or not nodeRight: return False
+        if nodeLeft.val != nodeRight.val: return False
+        
+        return (self.isMirror(nodeLeft.left, nodeRight.right)
+               and self.isMirror(nodeLeft.right, nodeRight.left))
+
+# iterative
+from collections import deque
+
+class Solution:
+    def isSymmetric(self, root: TreeNode) -> bool:
+        q = deque()
+        q.append(root)
+        q.append(root)
+        
+        while q:
+            node1 = q.popleft()
+            node2 = q.popleft()
+            
+            if (node1 is None and node2 is None): continue
+            if (node1 is None or node2 is None): return False
+            if (node1.val != node2.val): return False
+        
+            q.append(node1.left)
+            q.append(node2.right)
+            q.append(node1.right)
+            q.append(node2.left)
+        
+        return True
+        
diff --git a/leetcode/learn-cards/recursion-1/09_merge_two_sorted_lists.py b/leetcode/learn-cards/recursion-1/09_merge_two_sorted_lists.py
@@ -18,9 +18,6 @@ def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
 
 class Solution2:
     def mergeTwoLists(self, l1: ListNode, l2: ListNode) -> ListNode:
-        if not l1 or not l2:
-            return l1 or l2
-        
         dummy = ListNode(0)
         cur = dummy
         
