题解 | #在二叉树中找到两个节点的最近公共祖先#

import java.util.*;

/*
 * public class TreeNode {
 *   int val = 0;
 *   TreeNode left = null;
 *   TreeNode right = null;
 * }
 */

public class Solution {
    /**
     * 
     * @param root TreeNode类 
     * @param o1 int整型 
     * @param o2 int整型 
     * @return int整型
     */
    public int lowestCommonAncestor (TreeNode root, int o1, int o2) {
        // write code here
        if (root == null) {
            return -1;
        }
        return helper(root, o1, o2).val;
    }

    public TreeNode helper(TreeNode root, int o1, int o2) {
        if (root == null || root.val == o1 || root.val == o2) {
            return root;
        }
        TreeNode left = helper(root.left, o1, o2);
        TreeNode right = helper(root.right, o1, o2);
        if (left == null) {
            return right;
        }
        if (right == null) {
            return left;
        }
        return root;
    }
}