Submission #490325

#	Time	Username	Problem	Language	Result	Execution time	Memory
490325		XII	Tracks in the Snow (BOI13_tracks)	C++17	100 / 100	548 ms	160124 KiB

tracks

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

using ll = long long;

#define fi first
#define se second
#define mp make_pair
#define eb emplace_back
#define ALL(x) (x).begin(), (x).end()

#define FOR(i, a, b) for(int i = (a); i < (b); ++i)
#define FORU(i, a, b) for(int i = (a); i <= (b); ++i)
#define FORD(i, a, b) for(int i = (a); i >= (b); --i)

#define IOS cin.tie(0)->sync_with_stdio(false);
#define PROB "BOI13_tracks"
void Fi(){
    if(fopen(PROB".inp", "r")){
        freopen(PROB".inp", "r", stdin);
        freopen(PROB".out", "w", stdout);
    }
}

const int N = 4e3 + 1;
int a[N][N], n, m;
int d[N][N];

int encode(const char &c){
    switch(c){
        case '.': return 0;
        case 'F': return 1;
        case 'R': return -1;
    }
}

const int dx[] = {0, 0, -1, +1};
const int dy[] = {-1, +1, 0, 0};

using pi = pair<int, int>;
deque<pi> dq;

void bfs(const pi &s){
    dq.push_back(s); d[s.fi][s.se] = 1;
    while(!dq.empty()){
        auto [x, y] = dq.front(); dq.pop_front();
        FOR(direc, 0, 4){
            int i = x + dx[direc];
            int j = y + dy[direc];
            if(i < 1 || n < i || j < 1 || m < j) continue;
            if(!a[i][j] || d[i][j]) continue;
            if(a[i][j] != a[x][y]){
                d[i][j] = d[x][y] + 1;
                dq.push_back({i, j});
            } else{
                d[i][j] = d[x][y];
                dq.push_front({i, j});
            }
        }
    }
}

int main(){
    IOS;
    Fi();
    cin >> n >> m;
    FORU(i, 1, n){
        string s; cin >> s;
        FORU(j, 1, m){
            a[i][j] = encode(s[j - 1]);
        }
    }
    bfs({1, 1});
    int ans = 0;
    FORU(i, 1, n) FORU(j, 1, m) ans = max(ans, d[i][j]);
    cout << ans;
    return 0;
}

Compilation message (stderr)

tracks.cpp: In function 'void Fi()':
tracks.cpp:20:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   20 |         freopen(PROB".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
tracks.cpp:21:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   21 |         freopen(PROB".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
tracks.cpp: In function 'int encode(const char&)':
tracks.cpp:35:1: warning: control reaches end of non-void function [-Wreturn-type]
   35 | }
      | ^

• Subtask 1: 30 / 30
• Subtask 2: 70 / 70