/**
 * struct TreeNode {
 *	int val;
 *	struct TreeNode *left;
 *	struct TreeNode *right;
 * };
 */

class Solution {
public:
    /**
     * 
     * @param root TreeNode类 
     * @param o1 int整型 
     * @param o2 int整型 
     * @return int整型
     */
    int lowestCommonAncestor(TreeNode* root, int o1, int o2) {
        if (root == nullptr) return -1;
        if (root->val == o1 || root->val == o2) return root->val;
        int left_res = lowestCommonAncestor(root->left, o1, o2);
        int right_res = lowestCommonAncestor(root->right, o1, o2);
        if (left_res == -1) return right_res; // 若left为null,则在right
        if (right_res == -1) return left_res; // 若right为null,则在left
        // 二者都为null,则有一个节点在cur节点
        return root->val;
    }
};