#include "aoc.h"

namespace aoc2015 {

/* So, to find the second code (which ends up in row 2, column 1),
 * start with the previous value, 20151125.
 * Multiply it by 252533 to get 5088824049625. Then, divide that by 33554393,
 * which leaves a remainder of 31916031. That remainder is the second code.
 */
int64_t code_gen(int64_t code) {
  code *= 252533;
  code %= 33554393;
  return code;
}

// n = 0 ..
int64_t code_gen(int64_t code, size_t n) {
  while (n-- > 0) {
    code = code_gen(code);
  }
  return code;
}

// n = 1 ..
int64_t total_number_by(size_t n) {
  int64_t t{0};
  for (size_t i = 1; i <= n; i++) {
    t += i;
  }
  return t;
}

size_t row_number(int64_t r, int64_t c) { return r + c - 1; }

int64_t code_by(size_t r, size_t c) {
  size_t row = row_number(r, c);
  int64_t total = total_number_by(row - 1);

  for (size_t x = row; x >= 1; x--) {
    if (x == r) {
      return code_gen(20151125, total);
    }
    total += 1;
  }
  return 0;
}

// Enter the code at row 2947, column 3029.
std::pair<int64_t, int64_t> day25(line_view lv) {
  return {code_by(2947, 3029), 0};
}

} // namespace aoc2015