LCA of Binary Tree
描述
Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.
According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes v and w as the lowest node in T that has both v and w as descendants (where we allow a node to be a descendant of itself).”
_______3______
/ \
___5__ ___1__
/ \ / \
6 _2 0 8
/ \
7 4
For example, the lowest common ancestor (LCA) of nodes 5 and 1 is 3. Another example is LCA of nodes 5 and 4 is 5, since a node can be a descendant of itself according to the LCA definition.
分析
用自底向上(bottom-up)的思路,先看看是否能在root
的左子树中找到p
或q
,再看看能否在右子树中找到,
- 如果两边都能找到,说明当前节点就是最近公共祖先
- 如果左边没找到,则说明
p
和q
都在右子树 - 如果右边没找到,则说明
p
和q
都在左子树