Problem p00213 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <iostream>
#include <vector>

using vec = std::vector<int>;
using Land = std::vector<std::vector<int>>;

int W, H, N;
Land s;
std::vector<Land> res;

bool check(int h, int w, int a, int b, int num) {
  if (h + a > H || w + b > W) {
    return false;
  }
  for (int i = h; i < h + a; i++) {
    for (int j = w; j < w + b; j++) {
      if (s[i][j] != 0 && s[i][j] != num) {
        return false;
      }
    }
  }

  for (int i = 0; i < H; i++) {
    for (int j = 0; j < W; j++) {
      if (h <= i && i < h + a && w <= j && j < w + b) {
        continue;
      }
      if (s[i][j] == num) {
        return false;
      }
    }
  }

  return true;
}

void paint(int h, int w, int a, int b, int num) {
  for (int i = h; i < h + a; i++) {
    for (int j = w; j < w + b; j++) {
      s[i][j] = num;
    }
  }
}

void dfs(int idx, const vec &b, const vec &k) {
  if (idx == N) {
    res.emplace_back(s);
    return;
  }

  for (int i = 1; i <= k[idx]; i++) {
    int j = k[idx] / i;
    if (i * j != k[idx])
      continue;
    for (int h = 0; h < H; h++) {
      for (int w = 0; w < W; w++) {
        if (check(h, w, i, j, b[idx])) {
          auto tmp = s;
          paint(h, w, i, j, b[idx]);
          dfs(idx + 1, b, k);
          s = tmp;
        }
      }
    }
  }
}

void print(Land &l) {
  for (int i = 0; i < H; i++) {
    for (int j = 0; j < W; j++) {
      if (j > 0)
        std::cout << " ";
      std::cout << l[i][j];
    }
    std::cout << std::endl;
  }
}

void init() {
  s.assign(H, std::vector<int>(W));
  res.clear();
}

int main() {
  while (std::cin >> W >> H >> N, W) {
    init();
    vec b(N), k(N);
    for (int i = 0; i < N; i++) {
      std::cin >> b[i] >> k[i];
    }

    for (int i = 0; i < H; i++) {
      for (int j = 0; j < W; j++) {
        std::cin >> s[i][j];
      }
    }

    dfs(0, b, k);

    if (res.size() != 1) {
      std::cout << "NA" << std::endl;
    } else {
      print(res[0]);
    }
  }
  return 0;
}

Error: TLE

Fixed submission:

#include <iostream>
#include <vector>

using vec = std::vector<int>;
using Land = std::vector<std::vector<int>>;

int W, H, N;
Land s;
std::vector<Land> res;

bool check(int h, int w, int a, int b, int num) {
  if (h + a > H || w + b > W) {
    return false;
  }
  for (int i = h; i < h + a; i++) {
    for (int j = w; j < w + b; j++) {
      if (s[i][j] != 0 && s[i][j] != num) {
        return false;
      }
    }
  }
  return true;
}

void paint(int h, int w, int a, int b, int num) {
  for (int i = h; i < h + a; i++) {
    for (int j = w; j < w + b; j++) {
      s[i][j] = num;
    }
  }
}

void dfs(int idx, const vec &b, const vec &k) {
  if (idx == N) {
    res.emplace_back(s);
    return;
  }

  for (int i = 1; i <= k[idx]; i++) {
    int j = k[idx] / i;
    if (i * j != k[idx])
      continue;
    for (int h = 0; h < H; h++) {
      for (int w = 0; w < W; w++) {
        if (check(h, w, i, j, b[idx])) {
          auto tmp = s;
          paint(h, w, i, j, b[idx]);
          dfs(idx + 1, b, k);
          s = tmp;
        }
      }
    }
  }
}

void print(Land &l) {
  for (int i = 0; i < H; i++) {
    for (int j = 0; j < W; j++) {
      if (j > 0)
        std::cout << " ";
      std::cout << l[i][j];
    }
    std::cout << std::endl;
  }
}

void init() {
  s.assign(H, std::vector<int>(W));
  res.clear();
}

int main() {
  while (std::cin >> W >> H >> N, W) {
    init();
    vec b(N), k(N);
    for (int i = 0; i < N; i++) {
      std::cin >> b[i] >> k[i];
    }

    for (int i = 0; i < H; i++) {
      for (int j = 0; j < W; j++) {
        std::cin >> s[i][j];
      }
    }

    dfs(0, b, k);

    if (res.size() != 1) {
      std::cout << "NA" << std::endl;
    } else {
      print(res[0]);
    }
  }
  return 0;
}