class Solution {
public:
Node* connect(Node* root) {
if (!root) return NULL;
Node *p = root->next;
while (p) {
if (p->left) {
p = p->left;
break;
}
if (p->right) {
p = p->right;
break;
}
p = p->next;
}
if (root->right) root->right->next = p;
if (root->left) root->left->next = root->right ? root->right : p;
connect(root->right);
connect(root->left);
return root;
}
};
// Non-recursion, more than constant space
class Solution {
public:
Node* connect(Node* root) {
if (!root) return NULL;
queue<Node*> q;
q.push(root);
while (!q.empty()) {
int len = q.size();
for (int i = 0; i < len; ++i) {
Node *t = q.front(); q.pop();
if (i < len - 1) t->next = q.front();
if (t->left) q.push(t->left);
if (t->right) q.push(t->right);
}
}
return root;
}
};