A general purpose Segment Tree library

This library implements a general purpose Segment Tree data structure.

INSTRUCTIONS -

1. Include the header file "SEGTREE.h" in your header files directory and also in your code.

2. To construct the segment tree you need to initalize an object of SEGMENT_TREE and specify the following - 
   a. The datatype of the array/ vector. 
   b. The array/ vector of which you need to construct the tree. 
   c. An extravalue which is used to fill the remaining nodes of the segment tree. 
   d. A comparison function that detemines how the parent node is filled w.r.t left and right child nodes.

3. An example of creating a segment tree of type double with sum queries-

    double sum(double a, double b) { return a+b; }
    double extravalue = 0.0; 
    vector arr1 = {1.1,2.2,-5.4}; 
    double arr2[] = {1.1,2.2,-5.4}; 
    int size = 3; 
    
    with vector - SEGMENT_TREE<double> s(arr1,extravalue,sum); 
    with array - SEGMENT_TREE<double> s(arr2,size,extravalue,sum);

4. Functions include - 

   a. query(int leftindex, int rightindex) - returns a value according to comparison function; returns extravalue if invalid range. (0-based indexing)
   b. update(int index, datatype value) - updates the position index in the original array by value; leaves everything unchanged if invalid range. (0-based indexing)
   
5. Codeforces practice questions using above library - 
   
   a. https://codeforces.com/edu/course/2/lesson/4/1/practice/contest/273169/submission/88812979
   b. https://codeforces.com/edu/course/2/lesson/4/1/practice/contest/273169/submission/88812873