原題鏈接：https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/description/
代碼實現：

/**
 * Created by clearbug on 2018/2/26.
 */
public class Solution {

    public static void main(String[] args) {
        Solution s = new Solution();
//        System.out.println(s.lowestCommonAncestor());
    }

    public
 
 TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
        if (root == null || p == null || q == null) {
            return null;
        }

        if (p.val > q.val) { // just make p.val <= q.val; 這一步可以單獨抽出來，下面的遞歸邏輯單獨寫一個遞歸函數來
            TreeNode temp = p;
            p = q;
            q = temp;
        }

        if
 
 (root.val >= p.val && root.val <= q.val) {
            return root;
        }

        if (root.val > q.val) {
            return lowestCommonAncestor(root.left, p, q);
        }

        if (root.val < p.val) {
            return lowestCommonAncestor(root.right, p, q);
        }

        return
 
 null;
    }
}

235. Lowest Common Ancestor of a Binary Search Tree