C++二叉搜索树转化双向链表

/*
struct TreeNode {
	int val;
	struct TreeNode *left;
	struct TreeNode *right;
	TreeNode(int x) :
			val(x), left(NULL), right(NULL) {
	}
};*/
class Solution {
public:
    TreeNode *t;
    TreeNode* Convert(TreeNode* pRootOfTree) {
        if(!pRootOfTree) return nullptr;
        TreeNode *head = Convert(pRootOfTree->left);
        if(!head) head = pRootOfTree;
        pRootOfTree->left = t;
        if(t)
            t->right = pRootOfTree;
        t = pRootOfTree;
        Convert(pRootOfTree->right);
        return head;
    }
};