Задача про хорды

[Assasin92]

Помогли на другом форуме:

#include <iostream>
#include <fstream>
using namespace std;

int numOfDots, *firstArray, *sumArray, *s;

int prev(int x) { return (x & (x - 1)); }

int next(int x) { return ((x << 1) - (x & (x - 1))); }

int findSum(int left, int right) {
	int res = 0, x = right;
	for( ; x > 0; x = prev(x))
		res += s[x];

	for(x = left - 1; x > 0; x = prev(x))
		res -= s[x];

	return res;
}

void modify(int pos, int value) {
	sumArray[pos] += value;
	for(int x = pos; x < numOfDots; x = next(x))
		s[x] += value;
}

void getData() {
	int numOfChords, firstDot, secondDot;
	ifstream in("chords.in");
	in >> numOfChords;

	numOfDots = 2 * numOfChords + 1;
	firstArray = new int[numOfDots];
	sumArray = new int[numOfDots];
	s = new int[numOfDots];

	for(int i = 1, count = 0; count < numOfChords; ++count)
	{
		in >> firstDot >> secondDot;
		while (i < firstDot)
			++i;
		firstArray[i] = secondDot;
		firstArray[secondDot] = sumArray[i] = s[i] = 0;
	}
	in.close();
}

unsigned long check () {
	unsigned long res = 0;
	for (int i = 1; i < numOfDots; ++i)
		if (firstArray[i] != 0 && i + 1 != firstArray[i])
		{
			modify(firstArray[i], 1);
			res += findSum(i + 1, firstArray[i] - 1);
		}

	return res;
}

int main() {
	getData();
	ofstream out ("chords.out");
	out << check();
	out.close();
	return 0;
}

[Rin]

Эм, а где тут проверка на пересечение 2 хорд?