exercism/c/queen-attack/queen_attack.c

#include "queen_attack.h"

int same_position(position_t queen_1, position_t queen_2) {
  if (queen_1.row == queen_2.row && queen_1.column == queen_2.column) {
    return 1;
  }

  return 0;
}

int valid_position(position_t queen_1, position_t queen_2) {

  // Queens cannot occupy the same position
  if (same_position(queen_1, queen_2) ||
      // Make sure both queens are actually on the board
      (queen_1.row > 7 || queen_1.column > 7 || queen_2.row > 7 ||
       queen_2.column > 7)) {
    return 0;
  }

  return 1;
}

attack_status_t first_diagonal(position_t queen_1, position_t queen_2) {

  position_t pos = queen_1;
  while (pos.column <= 7) {

    if (pos.row == 0)
      break;

    pos.row -= 1;
    pos.column += 1;

    if (same_position(pos, queen_2)) {
      return CAN_ATTACK;
    }
  }

  return CAN_NOT_ATTACK;
}

attack_status_t second_diagonal(position_t queen_1, position_t queen_2) {

  position_t pos = queen_1;
  while (pos.row <= 7) {

    pos.row += 1;
    pos.column -= 1;

    if (same_position(pos, queen_2)) {
      return CAN_ATTACK;
    }
  }

  return CAN_NOT_ATTACK;
}

attack_status_t third_diagonal(position_t queen_1, position_t queen_2) {

  position_t pos = queen_1;
  for (int i = 0; i <= 7; i++) {

    if (pos.row == 0 || pos.column == 0)
      break;

    pos.row -= 1;
    pos.column -= 1;

    if (same_position(pos, queen_2)) {
      return CAN_ATTACK;
    }
  }
  return CAN_NOT_ATTACK;
}

attack_status_t fourth_diagonal(position_t queen_1, position_t queen_2) {

  position_t pos = queen_1;
  for (int i = 0; i <= 7; i++) {

    if (pos.row == 0 || pos.column == 0)
      break;

    pos.row -= 1;
    pos.column -= 1;

    if (same_position(pos, queen_2)) {
      return CAN_ATTACK;
    }
  }
  return CAN_NOT_ATTACK;
}

attack_status_t can_attack(position_t queen_1, position_t queen_2) {

  // Check both positions are valid
  if (!valid_position(queen_1, queen_2)) {
    return INVALID_POSITION;
  }

  // Attack - Queens occupy the same row or column
  if (queen_1.row == queen_2.row || queen_1.column == queen_2.column) {
    return CAN_ATTACK;
  }

  attack_status_t status = CAN_NOT_ATTACK;
  if (first_diagonal(queen_1, queen_2) == CAN_ATTACK ||
      second_diagonal(queen_1, queen_2) == CAN_ATTACK ||
      third_diagonal(queen_1, queen_2) == CAN_ATTACK ||
      fourth_diagonal(queen_1, queen_2) == CAN_ATTACK) {
    status = CAN_ATTACK;
  }

  return status;
}