算法导论程序32--红黑树的删除

红黑树的删除

class Node:
def __init__(self,key,right,left,p,color):
self.key=key
self.right=right
self.left=left
self.p=p
self.color=color

class tree:
def __init__(self,root,nil):
self.root=root
self.nil=nil
def tree_insert(self,z):
y=self.nil
x=self.root
while x!=self.nil:
y=x
if z.key<x.key:
x=x.left
else:
x=x.right
z.p=y
if y==self.nil:
self.root=z
elif z.key<y.key:
y.left=z
else:
y.right=z
z.left=self.nil
z.right=self.nil
z.color="RED"
self.rb_insert_fixup(z)
def left_rotate(self,x):
y=x.right
x.right=y.left
if y.left!=self.nil:
y.left.p=x
y.p=x.p
if x.p==self.nil:
self.root=y
elif x==x.p.left:
x.p.left=y
else:
x.p.right=y
y.left=x
x.p=y

def right_rotate(self,y):
x=y.left
y.left=x.right
if x.right!=self.nil:
x.right.p=y
x.p=y.p
if y.p==self.nil:
self.root=x
elif y==y.p.left:
y.p.left=x
else:
y.p.right=x
x.right=y
y.p=x

def rb_insert_fixup(self,z):
while z.p.color=="RED":
if z.p==z.p.p.left:
y=z.p.p.right
if y.color=="RED":
z.p.color="BLACK"
y.color="BLACK"
z.p.p.color="RED"
z=z.p.p
else:
if z==z.p.right:
z=z.p
self.left_rotate(z)
z.p.color="BLACK"
z.p.p.color="RED"
self.right_rotate(z.p.p)
else:
y=z.p.p.left
if y.color=="RED":
z.p.color="BLACK"
y.color="BLACK"
z.p.p.color="RED"
z=z.p.p
else:
if z==z.p.left:
z=z.p
self.right_rotate(z)
z.p.color="BLACK"
z.p.p.color="RED"
self.left_rotate(z.p.p)
self.root.color="BLACK"
def inorder_tree_walk(self,x):
if x!=self.nil:
self.inorder_tree_walk(x.left)
print(x.key)
self.inorder_tree_walk(x.right)
def tree_search(self,x,k):
if x==self.nil or k==x.key:
return x
if k < x.key:
return self.tree_search(x.left,k)
else: return self.tree_search(x.right,k)

def rb_transplant(self,u,v):
if u.p==self.nil:
self.root=v
elif u==u.p.left:
u.p.left=v
else:
u.p.right=v
v.p=u.p
def tree_minimum(self,x):
while x.left!=self.nil:
x=x.left
return x

def rb_delete(self,z):
y=z
y_original_color=y.color
if z.left==self.nil:
x=z.right
self.rb_transplant(z,z.right)
elif z.right==self.nil:
x=z.left
self.rb_transplant(z,z.left)
else:
y=self.tree_minimum(z.right)
y_original_color=y.color
x=y.right
if y.p==z:
x.p=y
else:
self.rb_transplant(y,y.right)
y.right=z.right
y.right.p=y
self.rb_transplant(z,y)
y.left=z.left
y.left.p=y
y.color=z.color
if y_original_color=="BLACK":
self.rb_delete_fixup(x)

def rb_delete_fixup(self,x):
while x!=self.root and x.color=="BLACK":
if x==x.p.left:
w=x.p.right
if w.color=="RED":
w.color="BLACK"
x.p.color="RED"
self.left_rotate(x.p)
w=x.p.right
if w.left.color=="BLACK" and w.right.color=="BLACK":
w.color="RED"
x=x.p
else:
if w.right.color=="BLACK":
w.left.color=="BLACK"
w.color="RED"
self.right_rotate(w)
w=x.p.right
w.color=x.p.color
x.p.color="BLACK"
w.right.color="BLACK"
self.left_rotate(x.p)
x=self.root
else:
w=x.p.left
if w.color=="RED":
w.color="BLACK"
x.p.color="RED"
self.right_rotate(x.p)
w=x.p.left
if w.right.color=="BLACK" and w.left.color=="BLACK":
w.color="RED"
x=x.p
else:
if w.left.color=="BLACK":
w.right.color=="BLACK"
w.color="RED"
self.left_rotate(w)
w=x.p.left
w.color=x.p.color
x.p.color="BLACK"
w.left.color="BLACK"
self.right_rotate(x.p)
x=self.root
x.color="BLACK"

运行结果：
>>> nil=Node(0,None,None,None,"BLACK")
>>> root=Node(7,nil,nil,nil,"BLACK")
>>> t=tree(root,nil)
>>> T=[4,18,3,6,11,19,2,9,14,22,12,17,20]
>>> for i in T:
z=Node(i,nil,nil,nil,"RED")
t.tree_insert(z)

>>> t.rb_delete(t.tree_search(t.root,4))

>>> t.root.left.key
3
>>> t.root.left.left.key
2
>>> t.root.left.right.key
6

>>> t.root.left.color
'BLACK'
>>> t.root.left.left.color
'BLACK'
>>> t.root.left.right.color
'BLACK'