Binary Indexed Tree role
Binary Indexed Tree (BIT) now used for the preamble and number of columns computationally efficient, and interval. It can be obtained in any of O (logn) time and preamble (prefix sum). As a array [2,5, -1,3,6], to calculate the second element and the fourth element: -1 + 5 + 3 = 7.
BIT holding portion by the respective sum nodes, then traversing the tree from the leaves to the root to obtain total sum.