步骤一：树的构建
字典
python
def createTree(arr1,arr2,tree):
if len(arr1)==0 and len(arr2)==0 :return
root = len(arr1)-1
# print(arr1[root],root)
flag = arr2.index(arr1[root])
# print(flag)
len_right = len(arr2)-flag-1
len_left = flag
if len(arr2[:flag])>=1:
lchild = arr1[flag-1]
else:
lchild = None
if len(arr2[flag+1:])>=1:
rchild = arr1[root-1]
else:
rchild = None
tree[arr1[root]] = {'lchild':None,'rchild':None}
tree[arr1[root]]['lchild'] = lchild
tree[arr1[root]]['rchild'] = rchild
# print(tree)
# print(arr1[:flag],arr1[len_left:len_left+len_right])
# print(arr2[:flag],arr2[flag+1:])
createTree(arr1[:flag],arr2[:flag],tree) # 左子树
createTree(arr1[len_left:len_left+len_right],arr2[flag+1:],tree) #右子树
tree = dict()
back = [3,4,2,6,5,1]
mid = [3,2,4,1,6,5]
createTree(back,mid,tree){1: {'lchild': 2, 'rchild': 5},
2: {'lchild': 3, 'rchild': 4},
3: {'lchild': None, 'rchild': None},
4: {'lchild': None, 'rchild': None},
5: {'lchild': 6, 'rchild': None},
6: {'lchild': None, 'rchild': None}}多级嵌套字典
python
def set_nested_dict_value(d, keys, value):
"""
根据键列表设置嵌套字典的值
:param d: 原始字典
:param keys: 键列表
:param value: 要设置的值
"""
# 从第一个键开始，逐层深入
for key in keys[:-1]:
# 如果当前键不存在，则创建一个空字典
if key not in d:
d[key] = {}
# 下一层字典
d = d[key]
# 设置最后一个键的值
d[keys[-1]] = value
def createTree(arr1,arr2,tree,step):
print('------------------------------------------')
# if len(arr1)==0 and len(arr2)==0 :
# print('结束')
# return
root = len(arr1)-1
print(arr1[root],root)
flag = arr2.index(arr1[root])
print(flag)
len_right = len(arr2)-flag-1
len_left = flag
if len(arr2[:flag])>=1:
lchild = arr1[flag-1]
else:
lchild = None
if len(arr2[flag+1:])>=1:
rchild = arr1[root-1]
else:
rchild = None
tmp = dict()
tmp['root'] = arr1[root]
if tmp['root']!= None:
tmp['lchild'] = {'root':lchild,'lchild':None,'rchild':None} if lchild != None else None
tmp['rchild'] = {'root':rchild,'lchild':None,'rchild':None} if rchild != None else None
print('tree',tree)
print('step',step)
if tree==dict():
tree.update(tmp)
else:
set_nested_dict_value(tree, step, tmp)
# print(tree)
# print(arr1[:flag],arr1[len_left:len_left+len_right])
# print(arr2[:flag],arr2[flag+1:])
# if len(arr1[:flag])>0 and len(arr2[:flag])>0:
# createTree(arr1[:flag],arr2[:flag],tree,step+['lchild']) # 左子树
# if len(arr1[len_left:len_left+len_right])>0 and len(arr2[flag+1:])>0:
# createTree(arr1[len_left:len_left+len_right],arr2[flag+1:],tree,step+['rchild']) #右子树
# if len(arr1[:flag])==0 and len(arr2[:flag])==0 and len(arr1[len_left:len_left+len_right])==0 and len(arr2[flag+1:])==0:
# print('chu')
# print(tree)
left_mid = arr2[:flag]
right_mid = arr2[flag+1:]
left_back = arr1[:flag]
right_back = arr1[len_left:len_left+len_right]
print(tree)
print(left_back,right_back)
print(left_mid,right_mid)
if len(left_back)>0 and len(left_mid)>0:
createTree(left_back,left_mid,tree,step+['lchild']) # 左子树
if len(right_back)>0 and len(right_mid)>0:
createTree(right_back,right_mid,tree,step+['rchild']) #右子树
if len(left_back)==0 and len(left_mid)==0 and len(right_back)==0 and len(right_mid)==0:
print('chu')
print(tree)
tree = dict()
back = [3,4,2,6,5,1]
mid = [3,2,4,1,6,5]
createTree(back,mid,tree,[])
tree简化
python
def set_nested_dict_value(d, keys, value):
"""
根据键列表设置嵌套字典的值
:param d: 原始字典
:param keys: 键列表
:param value: 要设置的值
"""
# 从第一个键开始，逐层深入
for key in keys[:-1]:
# 如果当前键不存在，则创建一个空字典
if key not in d:
d[key] = {}
# 下一层字典
d = d[key]
# 设置最后一个键的值
d[keys[-1]] = value
def createTree(arr1,arr2,tree,step):
root = len(arr1)-1
flag = arr2.index(arr1[root])
len_right = len(arr2)-flag-1
len_left = flag
tmp = {'root':arr1[root],'lchild':None,'rchild':None}
if tree==dict():
tree.update(tmp)
else:
set_nested_dict_value(tree, step, tmp)
left_mid = arr2[:flag]
right_mid = arr2[flag+1:]
left_back = arr1[:flag]
right_back = arr1[len_left:len_left+len_right]
if len(left_back)>0 and len(left_mid)>0:
createTree(left_back,left_mid,tree,step+['lchild']) # 左子树
if len(right_back)>0 and len(right_mid)>0:
createTree(right_back,right_mid,tree,step+['rchild']) #右子树
tree = dict()
back = [3,4,2,6,5,1]
mid = [3,2,4,1,6,5]
createTree(back,mid,tree,[])
tree{
'root': 1,
'lchild': {
'root': 2,
'lchild': {'root': 3, 'lchild': None, 'rchild': None},
'rchild': {'root': 4, 'lchild': None, 'rchild': None}},
'rchild': {
'root': 5,
'lchild': {'root': 6, 'lchild': None, 'rchild': None},
'rchild': None}
}步骤二：先序遍历
python
def preOrder(tree):
print(tree['root'])
if tree['lchild']:
preOrder(tree['lchild'])
if tree['rchild']:
preOrder(tree['rchild'])
preOrder(tree)1
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