题解 | #农场牛群族谱#

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
        if(root == null){
            return -1;
        }

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

        int left = lowestCommonAncestor(root.left,p,q);
        int right = lowestCommonAncestor(root.right,p,q);

        if(left >= 0 && right >= 0){
            return root.val;
        }

        return left >= 0?left:right;
    }
}