From eb99c7b66cd7c62f7a412c0bc4d96cd78aeb1ad2 Mon Sep 17 00:00:00 2001
From: shellfly <shell0fly@gmail.com>
Date: Wed, 23 Dec 2020 22:34:55 +0800
Subject: [PATCH] improve red black bst & fix typoes

---
 README.md                      | 2 +-
 algs4/edge_weighted_digraph.py | 8 ++++----
 algs4/red_black_bst.py         | 2 +-
 3 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/README.md b/README.md
index 90d1ad5..627ee99 100644
--- a/README.md
+++ b/README.md
@@ -20,7 +20,7 @@ pip install algs4
 ```
 
 ```python
-from algs4 import Stack
+from algs4.stack import Stack
 ```
 
 ## Index
diff --git a/algs4/edge_weighted_digraph.py b/algs4/edge_weighted_digraph.py
index 48c7957..27156ad 100644
--- a/algs4/edge_weighted_digraph.py
+++ b/algs4/edge_weighted_digraph.py
@@ -1,13 +1,13 @@
 """
- *  Execution:    python edge_weighted_graph.py filename.txt
+ *  Execution:    python edge_weighted_digraph.py filename.txt
  *  Data files:   https://algs4.cs.princeton.edu/43mst/tinyEWG.txt
  *                https://algs4.cs.princeton.edu/43mst/mediumEWG.txt
  *                https://algs4.cs.princeton.edu/43mst/largeEWG.txt
  *
- *  An edge-weighted undirected graph, implemented using adjacency lists.
+ *  An edge-weighted directed graph, implemented using adjacency lists.
  *  Parallel edges and self-loops are permitted.
  *
- *  % python edge_weighted_graph.py tinyEWD.txt
+ *  % python edge_weighted_digraph.py tinyEWD.txt
  * 8 vertices, 15 edges
  * 0: 0->2 0.26000 0->4 0.38000
  * 1: 1->3 0.29000
@@ -63,5 +63,5 @@ def edges(self):
 
 if __name__ == "__main__":
     import sys
-    graph = EdgeWeightedDiraph(file=open(sys.argv[1]))
+    graph = EdgeWeightedDigraph(file=open(sys.argv[1]))
     print(graph)
diff --git a/algs4/red_black_bst.py b/algs4/red_black_bst.py
index f32d22b..ef5239c 100644
--- a/algs4/red_black_bst.py
+++ b/algs4/red_black_bst.py
@@ -339,7 +339,7 @@ def _delete_min(self, h):
         return self.balance(h)
 
     def balance(self, h):
-        if self.is_red(h):
+        if self.is_red(h) and not self.is_red(h.left):
             h = self.rotate_left(h)
         if self.is_red(h.left) and self.is_red(h.left.left):
             h = self.rotate_right(h)