有一个排序二叉树，数据类型是int型，如何找出中间大的元素。

void tree2Dll(TNode* root, TNode*& tail) {
if (!root) {
return;
}
if (root->left) {
tree2Dll(root->left, tail);
}
TNode* tmp = root;
tmp->left = tail;
if (tail) {
tail->right = tmp;
}
tail = tmp;

if (root->right) {
tree2Dll(root->right, tail);
}
}

int findMedian(TNode* tail) {
if (!tail) {
return INT_MAX;
}

TNode* fast = tail;
TNode* slow = tail;
while (fast && slow) {
if (!(fast->left)) {
return slow->data;
} else if (fast->left && !(fast->left->left)) {
return (slow->data + slow->left->data) >> 1;
} else {
slow = slow->left;
fast = fast->left->left;
}
}
}