Completed s30 Trees-3

pathsum2.py

@@ -0,0 +1,31 @@
+class Solution:
+    def pathSum(self, root, targetSum):
+
+        result = []
+
+        def dfs(node, remaining, path):
+            if not node:
+                return
+
+            # choose
+            path.append(node.val)
+            remaining -= node.val
+
+            # leaf node
+            if not node.left and not node.right:
+                if remaining == 0:
+                    result.append(path[:])
+
+            # explore
+            dfs(node.left, remaining, path)
+            dfs(node.right, remaining, path)
+
+            # backtrack
+            path.pop()
+
+        dfs(root, targetSum, [])
+
+        return result
+
+# TC - O(h) h = height of tree because we only append valid path
+# SC - O(h) result is O(h) excluding path used for storing temporary paths

symmetrictree.py

@@ -0,0 +1,18 @@
+class Solution:
+    def isSymmetric(self, root):
+        if root is None:
+            return True
+        return self.helper(root.left, root.right)
+
+    def helper(self, left, right):
+        if left is None and right is None:
+            return True
+        if left is None or right is None:
+            return False
+        if left.val != right.val:
+            return False
+
+        return self.helper(left.left, right.right) and self.helper(left.right, right.left)
+
+# TC - O(n)
+# SC - O(h) where h - height of tree.