Create second-minimum-node-in-a-binary-tree.py

Author: kamyu104

Python/second-minimum-node-in-a-binary-tree.py

@@ -0,0 +1,32 @@
+# Time:  O(n)
+# Space: O(h)
+
+# Definition for a binary tree node.
+# class TreeNode(object):
+#     def __init__(self, x):
+#         self.val = x
+#         self.left = None
+#         self.right = None
+
+class Solution(object):
+    def findSecondMinimumValue(self, root):
+        """
+        :type root: TreeNode
+        :rtype: int
+        """
+        def findSecondMinimumValueHelper(root, max_heap, lookup):
+            if not root:
+                return
+            if root.val not in lookup:
+                heapq.heappush(max_heap, -root.val)
+                lookup.add(root.val)
+                if len(max_heap) > 2:
+                    lookup.remove(-heapq.heappop(max_heap))
+            findSecondMinimumValueHelper(root.left, max_heap, lookup)
+            findSecondMinimumValueHelper(root.right, max_heap, lookup)
+
+        max_heap, lookup = [], set()
+        findSecondMinimumValueHelper(root, max_heap, lookup)
+        if len(max_heap) < 2:
+            return -1
+        return -max_heap[0]