7.Populating Next Right Pointers in Each Node

Given a binary tree. Populate each next pointer to point to its next right node. If there is no next right node, the next pointer should be set to NULL.

Perfect Binary Tree

Binary Tree

Iterative Solution: (using Level Order Traversal)

class Solution
{
public:
    Node *connect(Node *root)
    {
        if (root == NULL)
        {
            return root;
        }
        queue<Node *> q;
        q.push(root);
        q.push(NULL);
        Node *t = NULL;

        while (!q.empty())
        {

            t = q.front();
            q.pop();

            if (t != NULL)
            {

                t->next = q.front();

                if (t->left)
                {
                    q.push(t->left);
                }
                if (t->right)
                {
                    q.push(t->right);
                }
            }

            else if (!q.empty())
            {
                q.push(NULL);
            }
        }

        return root;
    }
};

Time Complexity: O(n) , Space Complexity: O(n)

Solution II :