Added code for binary tree path sum

Binary tree path sum TheAlgorithms#7135

Author: trisha217

bt_path_sum.py

@@ -0,0 +1,10 @@
+def pathSum(self, root: TreeNode, target_sum: int) -> int:
+        def dfs(node: TreeNode, sums: List[int]) -> int:
+            if not node:
+                return 0
+            sums = [s + node.val for s in sums] + [node.val]
+            ans = sums.count(target_sum)
+            ans += dfs(node.left, sums) if node.left else 0
+            ans += dfs(node.right, sums) if node.right else 0
+            return ans
+        return dfs(root, [])