Data Structure Binary Search Tree: Inorder Successor in Binary Search Tree

 struct node {
     int val;
     node *left;
     node *right;
     node *parent;
     node() : val(), left(NULL), right(NULL) { }
     node(int v) : val(v), left(NULL), right(NULL) { }
 };

 node* insert(int n, node *root) {
     if (root == NULL) {
         root = new node(n);
         return root;
     }
     if (n < root->val) {
         if (root->left == NULL) {
             root->left = new node(n);
             return root->left;
         }
         else return insert(n, root->left);
     }
     if (n > root->val) {
         if (root->right == NULL) {
             root->right = new node(n);
             return root->right;
         }
         else return insert(n, root->right);
     }
 }

 //Variation: How would you find the sucessor of a node?
 node* leftmost(node *n) {
     if (n == NULL) return NULL;
     while (n->left) n = n->left;
     return n;
 }

 node* findSuccessor(node* n) {
     if (n == NULL) return NULL;
     if (!n->parent || n->right) return leftmost(n->right);
     else {
         while (n->parent && n->parent->right == n) n = n->parent;
         return n->parent;
     }
 }

下面是没有parent的代码

 node *minvalue(node *root) {
     while (root->left) root = root->left;
     return root;
 }

 node* successor(node *root, node *n) {
     if (n->right) return minvalue(n->right);
     node *succ = NULL;
     while (root) {
         if (n->data < root->data) {
             succ = root;
             root = root->left;
         }
         else if (n->data > root->data) root = root->right;
         else break;
     }
     return succ;
 }