Submission #757671

#	Time	Username	Problem	Language	Result	Execution time	Memory
757671		drdilyor	Tracks in the Snow (BOI13_tracks)	C++17	29.06 / 100	2110 ms	1048576 KiB

tracks

#include <bits/stdc++.h>

using namespace std;
using ll = long long;

signed main() {
    cin.tie(0)->sync_with_stdio(0);
    int n, m;
    cin >> n >> m;
    vector<string> mat(n);
    for (string& s : mat) {
        cin >> s;
    }
    auto id = [m](int i, int j) { return i* m + j;};
    vector<vector<pair<int,int>>> adj(n * m);

    for (int i = 0; i < n; i++) {
        for (int j = 0; j < m; j++) {
            for (auto [di, dj] : {pair{0, -1}, {0, 1}, {-1, 0}, {1, 0}}) {
                int ni = i + di;
                int nj = j + dj;
                if (clamp(ni, 0,n-1) == ni && clamp(nj, 0, m-1) == nj) {
                    if (mat[ni][nj] == '.' || mat[i][j] == '.') continue;
                    int c = mat[i][j] != mat[ni][nj];
                    adj[id(i, j)].push_back({id(ni, nj), c});
                }
            }
        }
    }

    static constexpr int inf = 1e9;
    vector<int> dist(n*m, inf), vis(n*m, 0);
    queue<int> cur, next;
    dist[0] = 0;
    cur.push(0);
    int res = 0;
    while (cur.size()) {
        int v = cur.front();
        vis[v] = 1;
        res = max(res, dist[v]);
        for (auto [e, ec]: adj[v]) {
            if (vis[e]) continue;
            dist[e] = min(dist[e], dist[v] + ec);
            if (ec) next.push(e);
            else cur.push(e);
        }
        cur.pop();
        if (cur.empty()) {
            cur.swap(next);
            next = {};
        }
    }
    cout << res+1 << '\n';
    

    return 0;
}

• Subtask 1: 5 / 30
• Subtask 2: 24.0625 / 70