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 {
    TreeNode commonA = null;
    /**
     * 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
        if (root == null){
            return -1;
        }
        if (p > q){
            int save = p;
            p = q;
            q = save;
        }
        preOrderFindAncestor(root, p, q);
        return commonA.val;
    }

    public void preOrderFindAncestor(TreeNode root, int p, int q){
        if (root == null){
            return;
        }
        if (root.val >= p && root.val <= q){
            commonA = root;
            return;
        }
        if (p < root.val && q < root.val){
            System.out.println(root.val);
            preOrderFindAncestor(root.left, p, q);
            return;
        }
        System.out.println(root.val);
        preOrderFindAncestor(root.right, p, q);
    }
}