mirror of
https://github.com/halfrost/LeetCode-Go.git
synced 2025-07-08 10:24:58 +08:00
63 lines
2.4 KiB
Markdown
Executable File
63 lines
2.4 KiB
Markdown
Executable File
# [1123. Lowest Common Ancestor of Deepest Leaves](https://leetcode.com/problems/lowest-common-ancestor-of-deepest-leaves/)
|
||
|
||
|
||
## 题目
|
||
|
||
Given a rooted binary tree, return the lowest common ancestor of its deepest leaves.
|
||
|
||
Recall that:
|
||
|
||
- The node of a binary tree is a *leaf* if and only if it has no children
|
||
- The *depth* of the root of the tree is 0, and if the depth of a node is `d`, the depth of each of its children is `d+1`.
|
||
- The *lowest common ancestor* of a set `S` of nodes is the node `A` with the largest depth such that every node in S is in the subtree with root `A`.
|
||
|
||
**Example 1:**
|
||
|
||
Input: root = [1,2,3]
|
||
Output: [1,2,3]
|
||
Explanation:
|
||
The deepest leaves are the nodes with values 2 and 3.
|
||
The lowest common ancestor of these leaves is the node with value 1.
|
||
The answer returned is a TreeNode object (not an array) with serialization "[1,2,3]".
|
||
|
||
**Example 2:**
|
||
|
||
Input: root = [1,2,3,4]
|
||
Output: [4]
|
||
|
||
**Example 3:**
|
||
|
||
Input: root = [1,2,3,4,5]
|
||
Output: [2,4,5]
|
||
|
||
**Constraints:**
|
||
|
||
- The given tree will have between 1 and 1000 nodes.
|
||
- Each node of the tree will have a distinct value between 1 and 1000.
|
||
|
||
|
||
## 题目大意
|
||
|
||
|
||
给你一个有根节点的二叉树,找到它最深的叶节点的最近公共祖先。
|
||
|
||
回想一下:
|
||
|
||
- 叶节点 是二叉树中没有子节点的节点
|
||
- 树的根节点的 深度 为 0,如果某一节点的深度为 d,那它的子节点的深度就是 d+1
|
||
- 如果我们假定 A 是一组节点 S 的 最近公共祖先,<font color="#c7254e" face="Menlo, Monaco, Consolas, Courier New, monospace">S</font> 中的每个节点都在以 A 为根节点的子树中,且 A 的深度达到此条件下可能的最大值。
|
||
|
||
|
||
提示:
|
||
|
||
- 给你的树中将有 1 到 1000 个节点。
|
||
- 树中每个节点的值都在 1 到 1000 之间。
|
||
|
||
|
||
## 解题思路
|
||
|
||
|
||
- 给出一颗树,找出最深的叶子节点的最近公共祖先 LCA。
|
||
- 这一题思路比较直接。先遍历找到最深的叶子节点,如果左右子树的最深的叶子节点深度相同,那么当前节点就是它们的最近公共祖先。如果左右子树的最深的深度不等,那么需要继续递归往下找符合题意的 LCA。如果最深的叶子节点没有兄弟,那么公共父节点就是叶子本身,否则返回它的 LCA。
|
||
- 有几个特殊的测试用例,见测试文件。特殊的点就是最深的叶子节点没有兄弟节点的情况。
|