题目
QQ20170107-164526.png
"""
Definition of TreeNode:
class TreeNode:
def __init__(self, val):
self.val = val
self.left, self.right = None, None
"""
class Solution:
# @param {TreeNode} root the root of the binary tree
# @return {List[str]} all root-to-leaf paths
def binaryTreePaths(self, root):
# Write your code here
# Write your code here
if root is None:
return []
stack = [root]#将root节点放入栈里面
result = []
while len(stack) != 0:#栈不为空就循环操作
topnode = stack[-1] #读取栈顶元素，但是将元素弹出
#从栈顶节点开始遍历子节点。直到寻找到叶子节点位置
while topnode.left is not None or topnode.right is not None:
if topnode.left is not None:#寻找过程中优先寻找位于左子树的节点
stack.append(topnode.left)
p = topnode.left
topnode.left = None #入栈后要置空，否则出栈的条件无法判断，或者可以寻找其他的办法标记哪些节点已经入过栈。
topnode = p
elif topnode.right is not None:
stack.append(topnode.right)
p = topnode.right
topnode.right = None
topnode = p
path = ""
#到这里表示已经寻找完一条路径，拼接字符串
for idx,node in enumerate(stack):
path += str(node.val)
if idx != len(stack)-1:
path += "->"
result.append(path)
#将最后一个节点出栈。一直寻找到没有入栈的节点。
while topnode.left is None and topnode.right is None:
stack.pop()
if len(stack) == 0:
return result
topnode = stack[-1]
return result
