Connect Nodes at Same Level
>

• Time : O(n)
• Space : O(d)

class Solution
{
    vector<Node*> lvl;
public:
    //Function to connect nodes at same level.
    void connect(Node *root, int dep = 0)
    {
        if(!root) return;
        if(lvl.size() == dep)
            lvl.push_back(root);
        else {
            lvl[dep]->nextRight = root;
            lvl[dep] = root;
        }
        connect(root->left, dep + 1);
        connect(root->right, dep + 1);
    }
};