I have found as explained in this article on HackerEarth that segment trees can be implemented by using arrays where child elements of a node positioned at array-index n are at indexes 2n and 2n+1.
Also it states that for storing n elements in my segment tree, I need 2n+1 nodes.
Yet recently when I solved few problems related to segment trees, sometimes my code gave runtime error which got resolved when I changed the array size for storing the segment tree to 4 x (size of array to be stored in segment tree). How can I be sure that a segment tree actually requires 4n-sized array for n elements.
If you are good at Russian, read this article: http://e-maxx.ru/algo/segment_tree
If you are not, I'll describe, what it is saying about: We need to notice, that the size of the array you contain the segment tree in, using such enumeration (where left child of i is 2i and right child is 2i+1), will be not 2n, but 4n. The thing is: this enumeration doesn't work completely fine when n is not a power of 2 - in this case we get "skipped" numbers, that are not assigned to any tree vertices (they mean "nodes"). Actually, it works as if we rounded n up to the closest power of 2. It doesn't make the implementation more complicated, but compels us to increase the size of the array to 4n.
Edit: Here is the English-version of the above-referenced article: https://cp-algorithms.com/data_structures/segment_tree.html