题目描述:
Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST.
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).”
_______6______ / \ ___2__ ___8__ / \ / \ 0 _4 7 9 / \ 3 5
For example, the lowest common ancestor (LCA) of nodes 2
and 8
is 6
. Another example is LCA of nodes 2
and 4
is 2
, since a node can be a descendant of itself according to the LCA definition.
这个题说的是二叉搜索树,找下规律。
如果p.val和q.val一个比root.val大,一个比root.val小,或者有一个等于根节点的val,那么根节点就是他们的最小共同父节点。
如果p.val和q,val都比root.val大,那么他们的最小共同父节点肯定在根节点的右侧。
如果p.val和q,val都比root.val小,那么他们的最小共同父节点肯定在根节点的左侧。
代码如下:
public class Solution { public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) { int num=(p.val-root.val)*(q.val-root.val); if(num<=0) return root; if(p.val-root.val>0) return lowestCommonAncestor(root.right, p, q); return lowestCommonAncestor(root.left, p, q); } }