开始刷leetcode day62:Lowest Common Ancestor of a Binary Search Tree

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.

Java:

/**

* Definition for a binary tree node.

* public class TreeNode {

* int val;

* TreeNode left;

* TreeNode right;

* TreeNode(int x) { val = x; }

* }

*/

public class Solution {

public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {

if(root == null) return null;

if(root.val == p.val || root.val == q.val) return root;

else

{

TreeNode node1 = lowestCommonAncestor(root.left,p,q);

TreeNode node2 = lowestCommonAncestor(root.right, p, q);

if(node1 != null && node2 != null) return root;

else return (node1 !=null)?node1:node2;

}

}

}

注意：如果node1和node2都不为null，意味着目前的root是他们的最low father