250312 합이 0인 네 정수

public static void main(String[] args) throws IOException {
	BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	int num = Integer.parseInt(br.readLine());
	int[][] map = readInput(br, num);

	sortColumns(map);
	int[] sum1 = computeSumArray(map, num, 0, 1);
	int[] sum2 = computeSumArray(map, num, 2, 3);

	Arrays.sort(sum1);
	Arrays.sort(sum2);

	long result = countZeroSums(sum1, sum2);
	System.out.println(result);
}

private static int[][] readInput(BufferedReader br, int num) throws IOException {
	int[][] map = new int[4][num];
	for (int i = 0; i < num; i++) {
		String[] values = br.readLine().split(" ");
		for (int j = 0; j < 4; j++) {
			map[j][i] = Integer.parseInt(values[j]);
		}
	}
	return map;
}

private static void sortColumns(int[][] map) {
	for (int j = 0; j < 4; j++) {
		Arrays.sort(map[j]);
	}
}

private static int[] computeSumArray(int[][] map, int num, int idx1, int idx2) {
	int[] sumArray = new int[num * num];
	int index = 0;
	for (int i = 0; i < num; i++) {
		for (int j = 0; j < num; j++) {
			sumArray[index++] = map[idx1][i] + map[idx2][j];
		}
	}
	return sumArray;
}

private static long countZeroSums(int[] sum1, int[] sum2) {
	int right = sum2.length - 1;
	long totalCount = 0;
	long sameValueCount = 0;

	for (int left = 0; left < sum1.length; left++) {
		if (left > 0 && sum1[left] == sum1[left - 1]) {
			totalCount += sameValueCount;
			continue;
		}
		sameValueCount = 0;

		while (right >= 0 && sum1[left] + sum2[right] > 0) {
			right--;
		}
		while (right >= 0 && sum1[left] + sum2[right] == 0) {
			sameValueCount++;
			right--;
		}
		totalCount += sameValueCount;
	}
	return totalCount;
}

출처:https://www.acmicpc.net/problem/7453