segment_tree.cpp

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#include <iostream>     
#include <vector>       
#include <algorithm>    
#include <cassert>      
 
/*
 * @namespace
 * @brief Data structures
 */
namespace data_structures {
template <class T>
class SegmentTree {
private:
    const T ID = 0;   
    std::vector<T> t; 
    int size = 0;     
private:
    T comb(T x, T y) {
        return x + y;
    }
    int mid(int l, int r) {
        return l + (r - l) / 2;
    }
    void update(int i, int l, int r, int pos, T val) {
        if(l == r) t[i] = val;
        else {
            int m = mid(l, r);
            if(pos <= m) update(i * 2, l, m, pos, val);
            else update(i * 2 + 1, m + 1, r, pos, val);
            t[i] = comb(t[i * 2], t[i * 2 + 1]);
        }
    }
    T range_comb(int i, int l, int r, int tl, int tr) {
        if(l == tl && r == tr) return t[i];
        if(tl > tr) return 0;
        int m = mid(l, r);
        return comb(range_comb(i * 2, l, m, tl, std::min(tr, m)), range_comb(i * 2 + 1, m + 1, r, std::max(tl, m + 1), tr));
    }
public:
    SegmentTree(int n) : t(n * 4, ID), size(n) {}
    void update(int pos, T val) {
        update(1, 1, size, pos, val);
    }
    T range_comb(int l, int r) {
        return range_comb(1, 1, size, l, r);
    }
};
} // namespace data_structures
 
static void test() {
    data_structures::SegmentTree<int> t(5);
    t.update(1, 1);
    t.update(2, 2);
    t.update(3, 3);
    t.update(4, 4);
    t.update(5, 5);
    assert(t.range_comb(1, 3) == 6); // 1 + 2 + 3 = 6
    t.update(1, 3);
    assert(t.range_comb(1, 3) == 8); // 3 + 2 + 3 = 8
 
    std::cout << "All tests have successfully passed!\n";
}
 
int main() {
    test();  // run self-test implementations
    return 0;
}