LeetCode 235. Lowest Common Ancestor of a Binary Search Tree

找最小公共祖先

递归：

只有两个点在根的两侧，他们的公共祖先必为当前根节点。

若同侧，则定义最新的根节点。递归直到两节点分开左右，或者其一节点为根节点

/**
* 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 (p.val < root.val && q.val < root.val) {
return lowestCommonAncestor(root.left, p, q);
} else if (p.val > root.val && q.val > root.val) {
return lowestCommonAncestor(root.right, p, q);
} else if ((p.val < root.val && q.val > root.val) || (p.val > root.val && q.val < root.val)) {
return root;
}
return root;
}
}