Submission #888764

#	Submission time	Handle	Problem	Language	Result	Execution time	Memory
888764	2023-12-18T07:34:07 Z	Billy_Nguyen	Mecho (IOI09_mecho)	C++17	100 / 100	221 ms	7280 KB

mecho

#include <bits/stdc++.h>
using namespace std;

const int MAX_N = 800;
vector < string > field (MAX_N);
int n, s;

bool
valid_sq (int x, int y)
{
  return x >= 0 && x < n && y >= 0 && y < n &&
    (field[x][y] == 'G' || field[x][y] == 'M');
}

bool
mecho_reached (int mecho_dis, int bees_dis)
{
  return mecho_dis / s < bees_dis;
}

int
main ()
{
  cin >> n >> s;
  queue < pair < int, int >>q;

  for (int i = 0; i < n; i++)
    {
      cin >> field[i];
    }

  vector < pair < int, int >>hives;
  int mechox, mechoy, home_x, home_y;
  // find x and y coordinates for for Mecho, the bees and the cave
  for (int i = 0; i < n; i++)
    {
      for (int j = 0; j < n; j++)
	{
	  if (field[i][j] == 'M')
	    {
	      mechox = i;
	      mechoy = j;
	    }
	  else if (field[i][j] == 'H')
	    {
	      hives.push_back (
				{
				i, j}
	      );
	    }
	  else if (field[i][j] == 'D')
	    {
	      home_x = i;
	      home_y = j;
	    }
	}
    }

  int dx[] = { -1, 0, 1, 0 };
  int dy[] = { 0, -1, 0, 1 };
  vector < vector < bool >> bees_visited (n, vector < bool > (n));
  vector < vector < int >>bees_time (n, vector < int >(n));


for (auto i:hives)
    {
      q.push (
	       {
	       i.first, i.second}
      );
      bees_visited[i.first][i.second] = true;
    }

  while (!q.empty ())
    {
      int x = q.front ().first, y = q.front ().second;
      q.pop ();
      for (int i = 0; i < 4; i++)
	{
	  int nx = x + dx[i], ny = y + dy[i];
	  if (valid_sq (nx, ny) && !bees_visited[nx][ny])
	    {
	      bees_time[nx][ny] = bees_time[x][y] + 1;
	      q.push (
		       {
		       nx, ny}
	      );
	      bees_visited[nx][ny] = true;
	    }
	}
    }

  // binary search on waiting time
  int l = 0;
  int r = n * n;
  while (l <= r)
    {
      vector < vector < bool >> mecho_visited (n, vector < bool > (n));
      vector < vector < int >>mecho_time (n, vector < int >(n));

      int eating_time = (l + r) / 2;

      // move bees


      // move Mecho
      q.push (
	       {
	       mechox, mechoy});
      mecho_visited[mechox][mechoy] = true;
      if (bees_time[mechox][mechoy] <= eating_time)
	{
	  q.pop ();
	}

      while (!q.empty ())
	{
	  int x = q.front ().first, y = q.front ().second;
	  q.pop ();
	  for (int i = 0; i < 4; i++)
	    {
	      int nx = x + dx[i], ny = y + dy[i];
	      /*
	       * check if mecho reaces node[x][y] before the bees
	       * divide the time mecho takes to reach a node by s, since
	       * mecho walks s steps at a time.
	       * substract the eating time from the time taken for the
	       * bees to reach the node, because that time was used by
	       * mecho for eating
	       */
	      if (valid_sq (nx, ny) && !mecho_visited[nx][ny] &&
		  mecho_reached (mecho_time[x][y] + 1,
				 bees_time[nx][ny] - eating_time))
		{
		  mecho_visited[nx][ny] = true;
		  q.push (
			   {
			   nx, ny}
		  );
		  mecho_time[nx][ny] = mecho_time[x][y] + 1;
		}
	    }
	}

      // check if mecho reached a node surrounding his cave before the bees
      bool reached = false;
      for (int i = 0; i < 4; i++)
	{
	  int nx = home_x + dx[i], ny = home_y + dy[i];
	  if (valid_sq (nx, ny) &&
	      mecho_reached (mecho_time[nx][ny],
			     bees_time[nx][ny] - eating_time) &&
	      mecho_visited[nx][ny])
	    {
	      reached = true;
	    }
	}
      if (reached)
	{
	  l = eating_time + 1;
	}
      else
	{
	  r = eating_time - 1;
	}
    }

  cout << l - 1 << '\n';
}

Compilation message

mecho.cpp: In function 'int main()':
mecho.cpp:110:27: warning: 'mechox' may be used uninitialized in this function [-Wmaybe-uninitialized]
  110 |       mecho_visited[mechox][mechoy] = true;
      |                           ^
mecho.cpp:149:29: warning: 'home_y' may be used uninitialized in this function [-Wmaybe-uninitialized]
  149 |    int nx = home_x + dx[i], ny = home_y + dy[i];
      |                             ^~
mecho.cpp:149:8: warning: 'home_x' may be used uninitialized in this function [-Wmaybe-uninitialized]
  149 |    int nx = home_x + dx[i], ny = home_y + dy[i];
      |        ^~

Subtask #1

100.0 / 100.0

#	Verdict	Execution time	Memory	Grader output
1	Correct	0 ms	344 KB	Output is correct
2	Correct	1 ms	348 KB	Output is correct
3	Correct	0 ms	348 KB	Output is correct
4	Correct	1 ms	344 KB	Output is correct
5	Correct	0 ms	348 KB	Output is correct
6	Correct	0 ms	348 KB	Output is correct
7	Correct	109 ms	7212 KB	Output is correct
8	Correct	1 ms	344 KB	Output is correct
9	Correct	1 ms	348 KB	Output is correct
10	Correct	0 ms	348 KB	Output is correct
11	Correct	0 ms	348 KB	Output is correct
12	Correct	1 ms	348 KB	Output is correct
13	Correct	1 ms	348 KB	Output is correct
14	Correct	1 ms	348 KB	Output is correct
15	Correct	0 ms	460 KB	Output is correct
16	Correct	0 ms	344 KB	Output is correct
17	Correct	0 ms	348 KB	Output is correct
18	Correct	1 ms	348 KB	Output is correct
19	Correct	0 ms	348 KB	Output is correct
20	Correct	1 ms	348 KB	Output is correct
21	Correct	0 ms	348 KB	Output is correct
22	Correct	0 ms	348 KB	Output is correct
23	Correct	1 ms	348 KB	Output is correct
24	Correct	1 ms	348 KB	Output is correct
25	Correct	1 ms	348 KB	Output is correct
26	Correct	1 ms	348 KB	Output is correct
27	Correct	1 ms	348 KB	Output is correct
28	Correct	1 ms	348 KB	Output is correct
29	Correct	1 ms	348 KB	Output is correct
30	Correct	1 ms	348 KB	Output is correct
31	Correct	1 ms	348 KB	Output is correct
32	Correct	1 ms	420 KB	Output is correct
33	Correct	7 ms	1800 KB	Output is correct
34	Correct	8 ms	1784 KB	Output is correct
35	Correct	26 ms	1800 KB	Output is correct
36	Correct	9 ms	2172 KB	Output is correct
37	Correct	10 ms	2136 KB	Output is correct
38	Correct	33 ms	2180 KB	Output is correct
39	Correct	12 ms	2628 KB	Output is correct
40	Correct	13 ms	2612 KB	Output is correct
41	Correct	48 ms	2632 KB	Output is correct
42	Correct	15 ms	3348 KB	Output is correct
43	Correct	16 ms	3300 KB	Output is correct
44	Correct	56 ms	3280 KB	Output is correct
45	Correct	18 ms	4052 KB	Output is correct
46	Correct	18 ms	3804 KB	Output is correct
47	Correct	65 ms	3812 KB	Output is correct
48	Correct	21 ms	4392 KB	Output is correct
49	Correct	23 ms	4432 KB	Output is correct
50	Correct	76 ms	4424 KB	Output is correct
51	Correct	26 ms	5012 KB	Output is correct
52	Correct	26 ms	5020 KB	Output is correct
53	Correct	98 ms	5064 KB	Output is correct
54	Correct	29 ms	5724 KB	Output is correct
55	Correct	31 ms	5732 KB	Output is correct
56	Correct	115 ms	5688 KB	Output is correct
57	Correct	33 ms	6440 KB	Output is correct
58	Correct	35 ms	6412 KB	Output is correct
59	Correct	135 ms	6400 KB	Output is correct
60	Correct	38 ms	7184 KB	Output is correct
61	Correct	40 ms	7236 KB	Output is correct
62	Correct	153 ms	7148 KB	Output is correct
63	Correct	117 ms	7172 KB	Output is correct
64	Correct	221 ms	7164 KB	Output is correct
65	Correct	190 ms	7140 KB	Output is correct
66	Correct	142 ms	7156 KB	Output is correct
67	Correct	133 ms	7164 KB	Output is correct
68	Correct	86 ms	7192 KB	Output is correct
69	Correct	76 ms	7224 KB	Output is correct
70	Correct	58 ms	7172 KB	Output is correct
71	Correct	63 ms	7192 KB	Output is correct
72	Correct	47 ms	7216 KB	Output is correct
73	Correct	52 ms	7208 KB	Output is correct
74	Correct	76 ms	7108 KB	Output is correct
75	Correct	97 ms	7280 KB	Output is correct
76	Correct	82 ms	7212 KB	Output is correct
77	Correct	100 ms	7228 KB	Output is correct
78	Correct	116 ms	7188 KB	Output is correct
79	Correct	66 ms	7196 KB	Output is correct
80	Correct	78 ms	7176 KB	Output is correct
81	Correct	93 ms	7236 KB	Output is correct
82	Correct	88 ms	7224 KB	Output is correct
83	Correct	111 ms	7192 KB	Output is correct
84	Correct	94 ms	7196 KB	Output is correct
85	Correct	103 ms	7184 KB	Output is correct
86	Correct	111 ms	7208 KB	Output is correct
87	Correct	101 ms	7216 KB	Output is correct
88	Correct	106 ms	7184 KB	Output is correct
89	Correct	101 ms	7216 KB	Output is correct
90	Correct	106 ms	7208 KB	Output is correct
91	Correct	104 ms	7228 KB	Output is correct
92	Correct	120 ms	7204 KB	Output is correct