Treap is a Cartesian tree（见Cartesian Tree） of (key,priority) pairs; it is heap-ordered according to the priority values, and an inorder traversal gives the keys in sorted order.
A Cartesian tree, in case of a sorted sequence, would be basically a linked list, making tree virtually useless. Treap is used to solve such cases by using random priority for each node.
Every node of Treap maintains two values.
1) Key Follows standard BST ordering (left is smaller and right is greater)
2) Priority Randomly assigned value that follows Max-Heap property.
In such implementation, X values are the keys (and at same time the values stored in the treap), and Y values are called priorities.
