python - 将二叉树转换为完整二叉树的函数?
问题描述
下面给出二叉树的实现。
class Node:
def __init__(self, data):
self.data = data
self.right = None
self.left = None
root = Node(5)
root.left = Node(2)
root.right = Node(3)
root.left.left = Node(7)
root.left.left.left = Node(9)
root.right.right = Node(1)
root.right.right.right = Node(6)
root.right.right.left = Node(4)
正如图像树中给出的那样,它不是一个完整的二叉树。如何编写一个函数来将上面的二叉树转换为完整的二叉树,只需将字符串数据节点添加到没有子节点的节点即可生成完整的二叉树。
Manualy 我将在代码中添加节点以获得这样的结果树:
root.left.right = Node('a')
root.right.left = Node('a')
root.right.left.left = Node('a')
root.right.left.right = Node('a')
root.left.right.right = Node('a')
root.left.right.left = Node('a')
但是如何编写一个函数来获取根节点并返回完整的二叉树。
解决方案
您将需要创建一个可以为您提供树中最大深度的方法。从那里您可以添加一个方法来递归地将空节点添加到该深度:
class Node:
def __init__(self, data):
self.data = data
self.right = None
self.left = None
@property
def maxDepth(self): # compute maximum depth (i.e. levels under self)
depth = 0
if self.left: depth = self.left.maxDepth+1
if self.right: depth = max(depth,self.right.maxDepth+1)
return depth
def expandToDepth(self,depth=None): # add empty nodes to fill tree
if depth is None: depth = self.maxDepth
if not depth: return
if not self.left: self.left = Node(None)
if not self.right: self.right = Node(None)
self.left.expandToDepth(depth-1)
self.right.expandToDepth(depth-1)
def __repr__(self): # this is just to print the tree
nodeInfo = lambda n: (str(n.data or "?"),n.left,n.right)
return "\n".join(printBTree(self,nodeInfo,isTop=False))
输出:
root = Node(5)
root.left = Node(2)
root.right = Node(3)
root.left.left = Node(7)
root.left.left.left = Node(9)
root.right.right = Node(1)
root.right.right.right = Node(6)
root.right.right.left = Node(4)
## BEFORE ##
print(root)
5
/ \
2 3
/ \
7 1
/ / \
9 4 6
root.expandToDepth()
## AFTER ##
print(root)
5
_____/ \_____
2 3
__/ \_ __/ \_
7 ? ? 1
/ \ / \ / \ / \
9 ? ? ? ? ? 4 6
printBTree()是我为回答另一个问题而提供的一个函数:https ://stackoverflow.com/a/49844237/5237560
这是它的副本(以防链接消失):
import functools as fn
def printBTree(node, nodeInfo=None, inverted=False, isTop=True):
# node value string and sub nodes
stringValue, leftNode, rightNode = nodeInfo(node)
stringValueWidth = len(stringValue)
# recurse to sub nodes to obtain line blocks on left and right
leftTextBlock = [] if not leftNode else printBTree(leftNode,nodeInfo,inverted,False)
rightTextBlock = [] if not rightNode else printBTree(rightNode,nodeInfo,inverted,False)
# count common and maximum number of sub node lines
commonLines = min(len(leftTextBlock),len(rightTextBlock))
subLevelLines = max(len(rightTextBlock),len(leftTextBlock))
# extend lines on shallower side to get same number of lines on both sides
leftSubLines = leftTextBlock + [""] * (subLevelLines - len(leftTextBlock))
rightSubLines = rightTextBlock + [""] * (subLevelLines - len(rightTextBlock))
# compute location of value or link bar for all left and right sub nodes
# * left node's value ends at line's width
# * right node's value starts after initial spaces
leftLineWidths = [ len(line) for line in leftSubLines ]
rightLineIndents = [ len(line)-len(line.lstrip(" ")) for line in rightSubLines ]
# top line value locations, will be used to determine position of current node & link bars
firstLeftWidth = (leftLineWidths + [0])[0]
firstRightIndent = (rightLineIndents + [0])[0]
# width of sub node link under node value (i.e. with slashes if any)
# aims to center link bars under the value if value is wide enough
#
# ValueLine: v vv vvvvvv vvvvv
# LinkLine: / \ / \ / \ / \
#
linkSpacing = min(stringValueWidth, 2 - stringValueWidth % 2)
leftLinkBar = 1 if leftNode else 0
rightLinkBar = 1 if rightNode else 0
minLinkWidth = leftLinkBar + linkSpacing + rightLinkBar
valueOffset = (stringValueWidth - linkSpacing) // 2
# find optimal position for right side top node
# * must allow room for link bars above and between left and right top nodes
# * must not overlap lower level nodes on any given line (allow gap of minSpacing)
# * can be offset to the left if lower subNodes of right node
# have no overlap with subNodes of left node
minSpacing = 2
rightNodePosition = fn.reduce(lambda r,i: max(r,i[0] + minSpacing + firstRightIndent - i[1]), \
zip(leftLineWidths,rightLineIndents[0:commonLines]), \
firstLeftWidth + minLinkWidth)
# extend basic link bars (slashes) with underlines to reach left and right
# top nodes.
#
# vvvvv
# __/ \__
# L R
#
linkExtraWidth = max(0, rightNodePosition - firstLeftWidth - minLinkWidth )
rightLinkExtra = linkExtraWidth // 2
leftLinkExtra = linkExtraWidth - rightLinkExtra
# build value line taking into account left indent and link bar extension (on left side)
valueIndent = max(0, firstLeftWidth + leftLinkExtra + leftLinkBar - valueOffset)
valueLine = " " * max(0,valueIndent) + stringValue
slash = "\\" if inverted else "/"
backslash = "/" if inverted else "\\"
uLine = "¯" if inverted else "_"
# build left side of link line
leftLink = "" if not leftNode else ( " " * firstLeftWidth + uLine * leftLinkExtra + slash)
# build right side of link line (includes blank spaces under top node value)
rightLinkOffset = linkSpacing + valueOffset * (1 - leftLinkBar)
rightLink = "" if not rightNode else ( " " * rightLinkOffset + backslash + uLine * rightLinkExtra )
# full link line (will be empty if there are no sub nodes)
linkLine = leftLink + rightLink
# will need to offset left side lines if right side sub nodes extend beyond left margin
# can happen if left subtree is shorter (in height) than right side subtree
leftIndentWidth = max(0,firstRightIndent - rightNodePosition)
leftIndent = " " * leftIndentWidth
indentedLeftLines = [ (leftIndent if line else "") + line for line in leftSubLines ]
# compute distance between left and right sublines based on their value position
# can be negative if leading spaces need to be removed from right side
mergeOffsets = [ len(line) for line in indentedLeftLines ]
mergeOffsets = [ leftIndentWidth + rightNodePosition - firstRightIndent - w for w in mergeOffsets ]
mergeOffsets = [ p if rightSubLines[i] else 0 for i,p in enumerate(mergeOffsets) ]
# combine left and right lines using computed offsets
# * indented left sub lines
# * spaces between left and right lines
# * right sub line with extra leading blanks removed.
mergedSubLines = zip(range(len(mergeOffsets)), mergeOffsets, indentedLeftLines)
mergedSubLines = [ (i,p,line + (" " * max(0,p)) ) for i,p,line in mergedSubLines ]
mergedSubLines = [ line + rightSubLines[i][max(0,-p):] for i,p,line in mergedSubLines ]
# Assemble final result combining
# * node value string
# * link line (if any)
# * merged lines from left and right sub trees (if any)
treeLines = [leftIndent + valueLine] + ( [] if not linkLine else [leftIndent + linkLine] ) + mergedSubLines
# invert final result if requested
treeLines = reversed(treeLines) if inverted and isTop else treeLines
# return intermediate tree lines or print final result
if isTop : print("\n".join(treeLines))
else : return treeLines
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