Codeforces/1829/e.cpp

#include <algorithm>
#include <cassert>
#include <cctype>
#include <cstdint>
#include <functional>
#include <iostream>
#include <optional>
#include <queue>
#include <sstream>
#include <string>
#include <vector>

namespace helpers {

using namespace std;

namespace math {
long pow(long base, long exp) {
  if (exp == 0) return 1;
  long half = pow(base, exp / 2);
  if (exp % 2 == 0) return half * half;
  return half * half * base;
}
}  // namespace math

namespace input {

template <typename T>
std::vector<T> load_vector(std::size_t size) {
  std::vector<T> result{};

  for (auto i = 0u; i < size; ++i) {
    T x;
    std::cin >> x;
    result.push_back(std::move(x));
  }

  return result;
}

}  // namespace input

namespace output {

template <typename T>
inline void answer(const T& ans) {
  cout << ans << "\n";
}

inline void yes() { cout << "YES\n"; }
inline void no() { cout << "NO\n"; }

inline void yesno(bool ans) {
  if (ans) {
    yes();
  } else {
    no();
  }
}

}  // namespace output

using namespace math;
using namespace input;
using namespace output;

#define LOOP(n) for (auto i = 0; i < n; ++i)

}  // namespace helpers

// for ‹N› test cases, uncomment for single test case
// #define SINGLE

namespace solution {

using namespace std;
using namespace helpers;

int run_bfs(vector<vector<int>>& grid, int y0, int x0) {
  int volume = 0;
  queue<pair<int, int>> q;

  // handle first element separately
  volume += grid[y0][x0];
  grid[y0][x0] = 0;
  q.push({y0, x0});

  while (q.size()) {
    auto [_y, _x] = q.front();
    q.pop();

    for (auto [dy, dx] :
         vector<pair<int, int>>{{-1, 0}, {1, 0}, {0, -1}, {0, 1}}) {
      auto y = _y + dy;
      auto x = _x + dx;

      if (y < 0 || y >= static_cast<int>(grid.size()) || x < 0 ||
          x >= static_cast<int>(grid[y].size()) || grid[y][x] == 0) {
        continue;
      }

      volume += grid[y][x];
      grid[y][x] = 0;
      q.push(pair{y, x});
    }
  }

  return volume;
}

int largest_volume(vector<vector<int>> grid) {
  int largest = 0;

  for (auto y = 0; y < static_cast<int>(grid.size()); ++y) {
    for (auto x = 0; x < static_cast<int>(grid[y].size()); ++x) {
      if (grid[y][x] == 0) {
        // ignore zeroes
        continue;
      }

      largest = max(largest, run_bfs(grid, y, x));
    }
  }

  return largest;
}

void solve() {
  int n, m;
  cin >> n >> m;

  vector<vector<int>> grid;
  LOOP(n) {
    auto row = load_vector<int>(m);
    grid.push_back(move(row));
  }

  answer(largest_volume(grid));
}

}  // namespace solution

using namespace solution;

#ifdef TEST

#include "../.common/cpp/catch_amalgamated.hpp"

TEST_CASE("examples") {
  CHECK(largest_volume(
            vector{vector{1, 2, 0}, vector{3, 4, 0}, vector{0, 0, 5}}) == 10);
  CHECK(largest_volume(vector<vector<int>>{vector{0}}) == 0);
  CHECK(largest_volume(vector{
            vector{0, 1, 1},
            vector{1, 0, 1},
            vector{1, 1, 1},
        }) == 7);
  CHECK(largest_volume(vector{
            vector{1, 1, 1, 1, 1},
            vector{1, 0, 0, 0, 1},
            vector{1, 0, 5, 0, 1},
            vector{1, 0, 0, 0, 1},
            vector{1, 1, 1, 1, 1},
        }) == 16);
  CHECK(largest_volume(vector{
            vector{1, 1, 1, 1, 1},
            vector{1, 0, 0, 0, 1},
            vector{1, 1, 4, 0, 1},
            vector{1, 0, 0, 0, 1},
            vector{1, 1, 1, 1, 1},
        }) == 21);
}

#else

int main(void) {

#ifdef SINGLE

  solution::solve();

#else

  // for multiple test cases
  int N;
  std::cin >> N >> std::ws;

  for (auto i = 0; i < N; ++i) {
    solution::solve();
  }

#endif

  return 0;
}

#endif