Create smallest-string-starting-from-leaf.py

Author: kamyu104

Python/smallest-string-starting-from-leaf.py

@@ -0,0 +1,31 @@
+# Time:  O(n + l * h), l is the number of leaves
+# 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 smallestFromLeaf(self, root):
+        """
+        :type root: TreeNode
+        :rtype: str
+        """
+        def dfs(node, candidate, result):
+            if not node:
+                return
+
+            candidate.append(chr(ord('a') + node.val))
+            if not node.left and not node.right:
+                result[0] = min(result[0], "".join(reversed(candidate)))
+            dfs(node.left, candidate, result)
+            dfs(node.right, candidate, result)
+            candidate.pop()
+
+        result = ["~"]
+        dfs(root, [], result)
+        return result[0]