题目链接 : https://leetcode-cn.com/problems/flatten-binary-tree-to-linked-list/
题目描述:
给定一个二叉树,原地将它展开为链表。
示例:
例如,给定二叉树
1
/ 2 5
/ \ 3 4 6
将其展开为:
1
2
3
4
5
6
思路:
其实对于这种题目,递归不太好想的,可以有个取巧的方法,就是把树转列表,因为结果是按照前序遍历的,所以有:
def flatten(self, root: TreeNode) -> None:
"""
Do not return anything, modify root in-place instead.
"""
if not root:return root
d = []
def helper(root):
if not root:
return
d.append(root.val)
helper(root.left)
helper(root.right)
helper(root)
i = 1
root.left = None
p = root
while i < len(d):
p.right = TreeNode(d[i])
p = p.right
i += 1
上面做法属于作弊过的,
思路一: 递归, 类似后序遍历
思路二: 迭代,
直接看代码,很容易理解,但是不容易想!
代码:
思路一:
def flatten(self, root: TreeNode, pre = None) -> None:
"""
Do not return anything, modify root in-place instead.
"""
# 类似后序遍历
def helper(root, pre):
if not root: return pre
# 记录遍历时候,该节点的前一个节点
pre = helper(root.right, pre)
pre = helper(root.left, pre)
# 拼接
root.right = pre
root.left = None
pre = root
return pre
helper(root, None)
java
class Solution {
public void flatten(TreeNode root) {
helper(root, null);
}
private TreeNode helper(TreeNode root, TreeNode pre) {
if (root == null) return pre;
pre = helper(root.right, pre);
pre = helper(root.left, pre);
root.right = pre;
root.left = null;
pre = root;
return pre;
}
}
思路二:
def flatten(self, root: TreeNode) -> None:
"""
Do not return anything, modify root in-place instead.
"""
cur = root
while cur:
if cur.left:
p = cur.left
while p.right: p = p.right
p.right = cur.right
cur.right = cur.left
cur.left = None
cur = cur.right
java
class Solution {
public void flatten(TreeNode root) {
TreeNode cur = root;
while (cur != null) {
if (cur.left != null) {
TreeNode p = cur.left;
while (p.right != null) p = p.right;
p.right = cur.right;
cur.right = cur.left;
cur.left = null;
}
cur = cur.right;
}
}
}
?
原文地址:https://www.cnblogs.com/powercai/p/11116688.html
时间: 2024-11-06 09:35:51