[IMP] Trees-3

path-sum-ii.py

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+''' 
+Time Complexity : O(n*h) 
+Space Complexity : O(n*h) 
+Did this code successfully run on Leetcode : Yes
+Any problem you faced while coding this :  No
+'''
+
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution:
+    def __init__(self):
+        self.result = []
+
+    def helper(self, root, currSum, targetSum, path):
+        # base
+        if root == None:
+            return
+
+        #logic
+        currSum += root.val
+        path.append(root.val)
+        #action
+        if root.left == None and root.right == None:
+            if currSum == targetSum:
+                self.result.append(list(path))
+
+        # recursion
+        self.helper(root.left, currSum, targetSum, path)
+        self.helper(root.right, currSum, targetSum, path)
+
+
+        #backtracking
+        path.pop(-1)
+
+    def pathSum(self, root: Optional[TreeNode], targetSum: int) -> List[List[int]]:
+        if root == None:
+            return self.result
+        self.helper(root, 0, targetSum, [])
+
+        return self.result
+

symmetric-tree.py

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+''' 
+Time Complexity : O(n) 
+Space Complexity : O(h) 
+Did this code successfully run on Leetcode : Yes
+Any problem you faced while coding this :  No
+'''
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution:
+    def __init__(self):
+        self.flag = True
+
+    def helper(self, left, right):
+        # base
+        if left is None and right is None:
+            return
+
+        if left is None or right is None or left.val != right.val:
+            self.flag = False
+            return
+
+        # logic
+        self.helper(left.left, right.right)
+        self.helper(left.right, right.left)
+
+    def isSymmetric(self, root: Optional[TreeNode]) -> bool:
+
+        self.helper(root.left, root.right)
+
+        return self.flag
+