我已经在Python中实现了树的前序遍历,但发现我的递归版本比迭代版本更快。
代码如下:
代码如下:
from __future__ import print_function
import time
class Tree():
def __init__(self, value):
self.value = value
self.left = None
self.right = None
def build_tree(string):
nodes = [0] + [Tree(s) for s in string]
for i in range(2, len(nodes)):
p = i/2
if i%2 == 0:
nodes[p].left = nodes[i]
else:
nodes[p].right = nodes[i]
return nodes[1]
def preorder(tree):
if tree:
# print(tree.value,end='')
preorder(tree.left)
preorder(tree.right)
def preorder2(tree):
t = tree
s = []
while t or s:
while t:
# print(t.value,end='')
s.append(t)
t = t.left
if s:
t = s.pop()
t = t.right
def main():
tree = build_tree('abcdefghi'*1000)
t = time.time()
for _ in range(100):
preorder(tree)
print(time.time() - t)
t = time.time()
for _ in range(100):
preorder2(tree)
print(time.time() - t)
if __name__ == '__main__':
main()
结果:
0.751042842865
1.0220580101
这意味着递归版本大约快25%。
我搜索了很多资料,每个人都说递归应该更慢,但我不明白为什么在我的代码中情况并非如此?
pop
或append
这样的方法调用导致递归版本更快吗?两种遍历的输出都相同,所以不是遍历顺序导致性能差异。 - Selçuk Cihan