답안 #488680

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
488680	2021-11-20T02:45:47 Z	nehasane	Mecho (IOI09_mecho)	C++14	100 / 100	613 ms	8392 KB

mecho

#include <bits/stdc++.h>
using namespace std;
const int MAX_N = 800;
vector <string> field(MAX_N);
bool bees_visited[MAX_N][MAX_N], mecho_visited[MAX_N][MAX_N];
//mecho_dis records the time taken for mecho to reach node[x][y].
//bees_dis does the same for the bees
int mecho_dis[MAX_N][MAX_N], bees_dis[MAX_N][MAX_N];
queue <pair <int, int>> q;
int dx[] = {-1, 1, 0, 0};
int dy[] = {0, 0, -1, 1};
int n, s;
bool valid_sq(int x, int y){
    if (x >= 0 && x < n && y >= 0 && y < n && (field[x][y] == 'G' || field[x][y] == 'M'))
        return true;
    return false;
}
int main()
{
    cin >> n >> s;
    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;
            }
        }
    }
    //binary search on waiting time
    int l = 0, r = n*n;
    while (l <= r){
        int eating_time = (l + r) / 2;
        memset(bees_visited, false, sizeof(bees_visited));
        memset(mecho_visited, false, sizeof(mecho_visited));
        memset(bees_dis, 0, sizeof(bees_dis));
        memset(mecho_dis, 0, sizeof(mecho_dis));
        //move bees
        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_dis[nx][ny] = bees_dis[x][y] + 1;    
                    q.push({nx, ny});
                    bees_visited[nx][ny] = true;
                }
            }
        }
        //move Mecho
        q.push({mechox, mechoy});
        mecho_visited[mechox][mechoy] = true;
        if (bees_dis[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_dis[x][y] + 1) / s < bees_dis[nx][ny] - eating_time){
                    mecho_visited[nx][ny] = true;
                    q.push({nx, ny});
                    mecho_dis[nx][ny] = mecho_dis[x][y] + 1;
                }
            }
        }
        //check if mecho reached a surrounding node before the bees
        bool mecho_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_dis[nx][ny] / s) < bees_dis[nx][ny] - eating_time
                && mecho_visited[nx][ny])
                mecho_reached = true;
        }
        if (mecho_reached)
            l = eating_time + 1;
        else
            r = eating_time - 1;
        }
    cout << l - 1 << '\n';
}

Compilation message

mecho.cpp: In function 'int main()':
mecho.cpp:67:36: warning: 'mechoy' may be used uninitialized in this function [-Wmaybe-uninitialized]
   67 |         if (bees_dis[mechox][mechoy] <= eating_time)
      |             ~~~~~~~~~~~~~~~~~~~~~~~^
mecho.cpp:67:36: warning: 'mechox' may be used uninitialized in this function [-Wmaybe-uninitialized]
mecho.cpp:91:37: warning: 'home_y' may be used uninitialized in this function [-Wmaybe-uninitialized]
   91 |             int nx = home_x+ dx[i], ny = home_y + dy[i];
      |                                     ^~
mecho.cpp:91:17: warning: 'home_x' may be used uninitialized in this function [-Wmaybe-uninitialized]
   91 |             int nx = home_x+ dx[i], ny = home_y + dy[i];
      |                 ^~

Subtask #1

100.0 / 100.0

#	결과	실행 시간	메모리	Grader output
1	Correct	4 ms	6480 KB	Output is correct
2	Correct	4 ms	6480 KB	Output is correct
3	Correct	4 ms	6480 KB	Output is correct
4	Correct	4 ms	6480 KB	Output is correct
5	Correct	4 ms	6480 KB	Output is correct
6	Correct	4 ms	6480 KB	Output is correct
7	Correct	478 ms	8088 KB	Output is correct
8	Correct	4 ms	6480 KB	Output is correct
9	Correct	5 ms	6552 KB	Output is correct
10	Correct	5 ms	6516 KB	Output is correct
11	Correct	4 ms	6480 KB	Output is correct
12	Correct	7 ms	6480 KB	Output is correct
13	Correct	7 ms	6564 KB	Output is correct
14	Correct	7 ms	6480 KB	Output is correct
15	Correct	6 ms	6480 KB	Output is correct
16	Correct	4 ms	6480 KB	Output is correct
17	Correct	6 ms	6480 KB	Output is correct
18	Correct	5 ms	6480 KB	Output is correct
19	Correct	5 ms	6480 KB	Output is correct
20	Correct	5 ms	6480 KB	Output is correct
21	Correct	5 ms	6480 KB	Output is correct
22	Correct	6 ms	6480 KB	Output is correct
23	Correct	6 ms	6480 KB	Output is correct
24	Correct	6 ms	6480 KB	Output is correct
25	Correct	7 ms	6480 KB	Output is correct
26	Correct	7 ms	6480 KB	Output is correct
27	Correct	6 ms	6608 KB	Output is correct
28	Correct	7 ms	6480 KB	Output is correct
29	Correct	7 ms	6488 KB	Output is correct
30	Correct	7 ms	6532 KB	Output is correct
31	Correct	6 ms	6480 KB	Output is correct
32	Correct	7 ms	6608 KB	Output is correct
33	Correct	37 ms	6864 KB	Output is correct
34	Correct	38 ms	6760 KB	Output is correct
35	Correct	73 ms	6864 KB	Output is correct
36	Correct	54 ms	6932 KB	Output is correct
37	Correct	48 ms	6928 KB	Output is correct
38	Correct	96 ms	6920 KB	Output is correct
39	Correct	59 ms	6992 KB	Output is correct
40	Correct	59 ms	6992 KB	Output is correct
41	Correct	120 ms	6992 KB	Output is correct
42	Correct	76 ms	7244 KB	Output is correct
43	Correct	75 ms	7276 KB	Output is correct
44	Correct	152 ms	7336 KB	Output is correct
45	Correct	90 ms	7388 KB	Output is correct
46	Correct	85 ms	7388 KB	Output is correct
47	Correct	171 ms	7376 KB	Output is correct
48	Correct	102 ms	7520 KB	Output is correct
49	Correct	108 ms	7504 KB	Output is correct
50	Correct	206 ms	7496 KB	Output is correct
51	Correct	122 ms	7608 KB	Output is correct
52	Correct	122 ms	7608 KB	Output is correct
53	Correct	268 ms	7608 KB	Output is correct
54	Correct	139 ms	7632 KB	Output is correct
55	Correct	140 ms	7632 KB	Output is correct
56	Correct	302 ms	7624 KB	Output is correct
57	Correct	160 ms	7832 KB	Output is correct
58	Correct	155 ms	7848 KB	Output is correct
59	Correct	363 ms	7852 KB	Output is correct
60	Correct	191 ms	7984 KB	Output is correct
61	Correct	176 ms	7956 KB	Output is correct
62	Correct	401 ms	8008 KB	Output is correct
63	Correct	487 ms	7972 KB	Output is correct
64	Correct	613 ms	8008 KB	Output is correct
65	Correct	539 ms	7996 KB	Output is correct
66	Correct	515 ms	8016 KB	Output is correct
67	Correct	507 ms	7964 KB	Output is correct
68	Correct	486 ms	8016 KB	Output is correct
69	Correct	496 ms	7996 KB	Output is correct
70	Correct	461 ms	8016 KB	Output is correct
71	Correct	480 ms	7888 KB	Output is correct
72	Correct	451 ms	7996 KB	Output is correct
73	Correct	437 ms	8268 KB	Output is correct
74	Correct	480 ms	8272 KB	Output is correct
75	Correct	490 ms	8268 KB	Output is correct
76	Correct	450 ms	8272 KB	Output is correct
77	Correct	488 ms	8392 KB	Output is correct
78	Correct	472 ms	8232 KB	Output is correct
79	Correct	460 ms	8232 KB	Output is correct
80	Correct	478 ms	8232 KB	Output is correct
81	Correct	480 ms	8264 KB	Output is correct
82	Correct	493 ms	8228 KB	Output is correct
83	Correct	502 ms	8192 KB	Output is correct
84	Correct	482 ms	8192 KB	Output is correct
85	Correct	508 ms	8144 KB	Output is correct
86	Correct	489 ms	8188 KB	Output is correct
87	Correct	494 ms	8192 KB	Output is correct
88	Correct	476 ms	8132 KB	Output is correct
89	Correct	495 ms	8264 KB	Output is correct
90	Correct	479 ms	8144 KB	Output is correct
91	Correct	496 ms	8252 KB	Output is correct
92	Correct	505 ms	8180 KB	Output is correct