alexandervasyuk

public int matrixRegionSumNaive(int[][] matrix, Coordinate A, Coordinate D) {
  int result = 0;
  for (int j = A.y; j < matrix.length; j++) {
    for (int i = A.x; i < matrix[0].length; i++) {
      result += matrix[i][j];
    }
  }
  return result;
}

alexandervasyuk

public static List<Pair> pairsThatSumUpToK(int[] a, int k) {
	HashSet<Integer> set = new HashSet<Integer>();
	List<Pair> result = new ArrayList<Pair>();
	for (int i = 0 ; i < a.length; i++) {
		int lookup = k - i;
		if (set.contains(lookup)) {
			result.add(new Pair(lookup, i));
		} else {
			set.add(i);
		}

alexandervasyuk

public static List<Pair> pairsThatSumUpToK(int[] a, int k) {
    Arrays.sort(a);
	List<Pair> result = new ArrayList<Pair>();
	int left = 0;
	int right = a.length-1;
	
	while(left < right) {
		int sum = a[left] + a[right];
		if (sum < k) left++;
		else if (sum > k) right--;

alexandervasyuk

public Node partition(Node node, int x) {
    Node lessHead, lessTail, greaterHead, greaterTail;

    while (node != null) {
        Node next = node.next;
        node.next = null;
        if (node.data < x) {
            if (lessHead == null) {
                lessHead = lessTail = node;
            } else {