// If a cell is zero, the row and column are set to zero.

#define CATCH_CONFIG_MAIN
#include <catch.hpp>

#include <fmt/format.h>
#include <experimental/string_view>
#include <string>
#include <unordered_set>

using string_view = std::experimental::string_view;

using matrix = std::array<std::array<char, 4>, 3>;

template <typename T>
std::string to_string(const T& img) {
  std::string out;

  for (const auto& row : img) {
    for (auto ch : row) {
      out.push_back(ch);
    }
    out.push_back(';');
  }
  return out;
}

void fill(matrix& m) {
  for (auto& row : m) {
    for (auto& ch : row) {
      ch = '1';
    }
  }
}

void clear(matrix& m) {
  // Record the rows and cols that have a zero in them.
  std::unordered_set<size_t> rows;
  std::unordered_set<size_t> cols;

  for (size_t y = 0; y < m.size(); y++) {
    auto& row = m[y];

    for (size_t x = 0; x < row.size(); x++) {
      if (row[x] == '0') {
        cols.insert(x);
        rows.insert(y);
      }
    }
  }

  // Now go and clear the rows and cols.
  for (auto y : rows) {
    for (auto& ch : m[y]) {
      ch = '0';
    }
  }

  for (auto x : cols) {
    for (auto& row : m) {
      row[x] = '0';
    }
  }
}

TEST_CASE("cc18", "zeros") {
  matrix m;
  fill(m);

  CHECK(to_string(m) == "1111;1111;1111;");

  m[0][1] = '0';
  CHECK(to_string(m) == "1011;1111;1111;");

  clear(m);
  CHECK(to_string(m) == "0000;1011;1011;");

  fill(m);
  m[0][0] = '0';
  m[2][3] = '0';
  clear(m);
  CHECK(to_string(m) == "0000;0110;0000;");
}