제출 #917216

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
917216		vanea	Mecho (IOI09_mecho)	C++14	95 / 100	157 ms	8304 KiB

mecho

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

const int mxN = 801;
int n, s;
vector<string> field(mxN);
bool vis1[mxN][mxN], vis2[mxN][mxN];
int d1[mxN][mxN], d2[mxN][mxN];

vector<int> xy = {1, 0, -1, 0}, yx = {0, 1, 0, -1};

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

void bfs1(queue<array<int, 2>> &q) {
    while(!q.empty()) {
        auto x = q.front()[0], y = q.front()[1];
        q.pop();
        for(int k = 0; k < 4; k++) {
            int a = x + xy[k], b = y + yx[k];
            if(valid(a, b) && !vis1[a][b]) {
                vis1[a][b] = true; d1[a][b] = d1[x][y]+1;
                q.push({a, b});
            }
        }
    }
}

bool reaches(int a, int b) {
    return a/s < b;
}

void bfs2(queue<array<int, 2>> &q, int t) {
    while(!q.empty()) {
        auto x = q.front()[0], y = q.front()[1];
        q.pop();
        for(int k = 0; k < 4; k++) {
            int a = x + xy[k], b = y + yx[k];
            if(valid(a, b) && !vis2[a][b] && reaches(d2[x][y]+1, d1[a][b] - t)) {
                vis2[a][b] = true;
                d2[a][b] = d2[x][y] + 1;
                q.push({a, b});
            }
        }
    }
}

void restart() {
    memset(vis2, false, sizeof vis2);
    memset(d2, 0, sizeof d2);
}

int main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cin >> n >> s;
    vector<array<int, 2>> hives;
    array<int, 2> start, finish;
    for(int i = 0; i < n; i++) {
        cin >> field[i];
        for(int j = 0; j < n; j++) {
            if(field[i][j] == 'M') {
                start = {i, j};
            }
            else if(field[i][j] == 'H') {
                hives.push_back({i, j});
            }
            else if(field[i][j] == 'D') {
                finish = {i, j};
            }
        }
    }
    queue<array<int, 2>> q;
    for(auto it : hives) {
        q.push(it);
        vis1[it[0]][it[1]] = true;
    }
    bfs1(q);
    int l = 0, r = n*n;
    while(l <= r) {
        int mid = (l+r)/2;
        restart();
        q.push(start);
        if(d1[start[0]][start[1]] <= mid) q.pop();
        vis2[start[0]][start[1]] = true;
        bfs2(q, mid);
        bool can = false;
        for(int k = 0; k < 4; k++) {
            int a = finish[0] + xy[k], b = finish[1] + yx[k];
            if(valid(a, b) && vis2[a][b]) {
                can = true;
            }
        }
        if(can) l = mid+1;
        else r = mid-1;
    }
    cout << l-1;
}

컴파일 시 표준 에러 (stderr) 메시지

mecho.cpp: In function 'int main()':
mecho.cpp:93:60: warning: 'finish.std::array<int, 2>::_M_elems[1]' may be used uninitialized in this function [-Wmaybe-uninitialized]
   93 |             int a = finish[0] + xy[k], b = finish[1] + yx[k];
      |                                                            ^
mecho.cpp:93:37: warning: 'finish.std::array<int, 2>::_M_elems[0]' may be used uninitialized in this function [-Wmaybe-uninitialized]
   93 |             int a = finish[0] + xy[k], b = finish[1] + yx[k];
      |                                     ^

• Subtask 1: 95 / 100