Category
algorithm
First Missing Positive
The problem requires finding the smallest positive integer that doesn't appear in an unsorted array 
Binary Indexed Tree (Fenwick Tree)
A Fenwick tree or binary indexed tree (BIT) is a data structure that can efficiently update elements and calculate prefix sums in a table of numbers 
Collection of bit mask operation
I have collected a few popular and useful bit operations 
Modular Inverse
In arithmetic, a modular multiplicative inverse of an integer a is an integer x such that the product a*x = 1 with respect to the modulus m -
Subarray Sums Divisible by K
Given an array of integers and an integer k, the problem is to find the total number of continuous subarrays whose sum is divisible by k