Submission #1043878

#	Time	Username	Problem	Language	Result	Execution time	Memory
1043878		daviedu	Tracks in the Snow (BOI13_tracks)	C++17	100 / 100	556 ms	88908 KiB

tracks

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

#define fastio ios_base::sync_with_stdio(0); cin.tie(0)
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define ll long long

struct P{
    ll x, y;
};

void dbg_out() { cerr << endl; }
template <typename H, typename... T>
void dbg_out(H h, T... t) { cerr << ' ' << h; dbg_out(t...); }
#define dbg(...) { cerr << #__VA_ARGS__ << ':'; dbg_out(__VA_ARGS__); }


const int N = 4001;
char grid[N][N];
int dist[N][N];
int h, w;

int valid(int x, int y){
    return (0 <= x && x < h) && (0 <= y && y < w);
}

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

signed main(){
    fastio;
    cin >> h >> w;
    for (int i=0; i<h; i++){
        for (int j=0; j<w; j++){
            cin >> grid[i][j];
        }
    }

    memset(dist, -1, sizeof(dist));
    int ans=1;
    queue<pair<int, int>> q0, q1;
    dist[0][0] = 1;
    q0.push({0, 0});
    int x, y;
    int ctr=0;
    while (!q0.empty() || !q1.empty()){
        while (!q0.empty()){
            tie(x, y) = q0.front(); q0.pop();
            ans = max(ans, dist[x][y]);
            for (int i=0; i<4; i++){
                int a, b;
                a = dx[i]+x;
                b = dy[i]+y;
                if (!valid(a, b) || grid[a][b] == '.' || dist[a][b] != -1) continue;
                dist[a][b] = dist[x][y];
                if (grid[a][b] != grid[x][y]){
                    dist[a][b]++;
                    q1.push({a, b});
                }
                else q0.push({a, b});
            }
        }
        swap(q0, q1);
    }

    cout << ans << '\n';
}

Compilation message (stderr)

tracks.cpp: In function 'int main()':
tracks.cpp:46:9: warning: unused variable 'ctr' [-Wunused-variable]
   46 |     int ctr=0;
      |         ^~~

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