题解 | #二叉搜索树的最近公共祖先#

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 *   public TreeNode(int val) {
 *     this.val = val;
 *   }
 * }
 */

public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 
     * @param p int整型 
     * @param q int整型 
     * @return int整型
     */
    public int lowestCommonAncestor (TreeNode root, int p, int q) {
        // write code here
        TreeNode ancestor = commonAncestor(root, p, q);
        if (ancestor == null) {
            return -1;
        }
        return ancestor.val;
    }

    public TreeNode commonAncestor(TreeNode root, int p, int q) {
        if (root == null) {
            return null;
        }
        if (root.val == p && root.val == q) {
            return root;
        }
        if (root.val > p && root.val > q) {
            return commonAncestor(root.left, p, q);
        }
        if (root.val < p && root.val < q) {
            return commonAncestor(root.right, p, q);
        }
        return root;
    }
}