每一个节点当做最大拓扑结构的头节点，遍历完所有的节点即可

struct TreeNode {
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode() { val = 0, left = nullptr, right = nullptr; }
};

// 判断node是否在以root为头节点的搜索二叉树上
bool isBSTNode(TreeNode *root, TreeNode *node) {
    if (!root) return false;
    if (root == node) return true;
    return isBSTNode( (root->val > node->val) ? root->left : root->right, node);
}

// 搜索以root为头节点的最大拓扑结构
int getSizeFromNode(TreeNode *root, TreeNode *cur) {
    if (!root || !cur) return 0;
    if (!isBSTNode(root, cur)) return 0;
    // 以root为头节点的满足要求，继续从左右子树开始搜索
    return 1 + getSizeFromNode(root, cur->left) + getSizeFromNode(root, cur->right);
}

void getMaxTopSize(TreeNode *root,int &ans) {
    if (!root) return;
    ans = max(ans, getSizeFromNode(root, root));
    getMaxTopSize(root->left, ans);
    getMaxTopSize(root->right, ans);
}

int main()
{
#ifdef LOCAL
    freopen("../leetcode/in.txt", "r", stdin);
#endif

    int n, root, ans = 0;
    int rt, l, r;
    cin >> n >> root;
    vector<TreeNode> tree(n + 1);
    for (int i = 0; i < n; i++) {
        cin >> rt >> l >> r;
        tree[rt].val = rt;
        if (l) tree[rt].left = &tree[l];
        if (r) tree[rt].right = &tree[r];
    }
    getMaxTopSize(&tree[root], ans);
    cout << ans << endl;
    return 0;
}