Divide & Conquer: Count Inversions

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

typedef unsigned long long ull;

const int MAX_SIZE = 100000;
int data[MAX_SIZE];
int sz;

void loadData() {
	ifstream ifs("in.txt");
	if(ifs.is_open()) {
		int x;
		int i = 0;
		while(ifs >> x) {
			data[i] = x;
			i++;
		}
		sz = i;
	}
}

ull countSplitInversions(int a, int b) {
	ull ret = 0;
	
	int median = (a+b)/2;
	
	int i = a;
	int j = median + 1;
	
	int len = b - a + 1;
	int* temp_array = new int[len];
	
	for(int idx = 0; idx < len; idx++)
	{
		if(i > median)
		{
			temp_array[idx] = data[j];
			j++;
			continue;
		}
		
		if(j > b)
		{
			temp_array[idx] = data[i];
			i++;
			continue;
		}
		
		if(data[i] <= data[j])
		{
			temp_array[idx] = data[i];
			i++;
		}
		
		if(data[i] > data[j])
		{
			temp_array[idx] = data[j];
			
			ret += median - i + 1;
			
			j++;
		}

	}
	
	int temp_idx = 0;
	for(int idx = a; idx <= b; idx++)
	{
		data[idx] = temp_array[temp_idx];
		temp_idx++;
	}
	
	return ret;
}

ull countInversions(int a, int b) {
	// base case
	if(b < a){
		return 0;
	}
	
	// base case
	if(b == a)
	{
		return 0;
	}
	
	int median = (a+b) / 2;
	ull l = countInversions(a, median);
	ull r = countInversions(median+1, b);
	ull s = countSplitInversions(a, b); 
	
	return l+r+s;
}

int main() {
	loadData();
	cout << countInversions(0, sz-1) << endl;
	return 0;
}