Submission #1139526

#	Time	Username	Problem	Language	Result	Execution time	Memory
1139526		anmattroi	Tracks in the Snow (BOI13_tracks)	C++17	100 / 100	1060 ms	632460 KiB

tracks

#include <bits/stdc++.h>
#define maxn 4005
#define fi first
#define se second
using namespace std;
using ii = pair<int, int>;

int n, m;
char a[maxn][maxn];
int cl[maxn][maxn];

int dv[4] = {0, 1, 0, -1};
int dh[4] = {1, 0, -1, 0};

int par[maxn*maxn];
int nho[maxn*maxn], id = 0;

int find_set(int v) {
    return par[v] < 0 ? v : par[v] = find_set(par[v]);
}

void union_set(int u, int v) {
    u = find_set(u); v = find_set(v);
    if (u == v) return;
    if (par[u] < par[v]) swap(u, v);
    par[v] += par[u];
    par[u] = v;
}

bool ok(int i, int j) {
    return (1 <= i && i <= n && 1 <= j && j <= m);
}
int rem[maxn*maxn];

vector<int> adj[maxn*maxn];

void bfs(int ox, int oy) {
    queue<ii> q;
    q.push(ii{ox, oy});
    cl[ox][oy] = ++id;
    vector<int> nodes;
    while (!q.empty()) {
        auto [u, v] = q.front(); q.pop();
        for (int k = 0; k < 4; k++) {
            int i = u + dv[k], j = v + dh[k];
            if (!ok(i, j)) continue;
            if (a[i][j] != a[u][v] && a[i][j] != '.') {
                if (cl[i][j] && !rem[cl[i][j]]) {
                    rem[cl[i][j]] = 1;
                    adj[cl[i][j]].emplace_back(id);
                    adj[id].emplace_back(cl[i][j]);
                    nodes.emplace_back(cl[i][j]);
                }
            } else if (a[i][j] == a[u][v] && !cl[i][j]) {
                cl[i][j] = id;
                q.push(ii{i, j});
            }

        }
    }
    for (int i : nodes) rem[i] = 0;

}


int main() {
    ios::sync_with_stdio(false);
    cin.tie(NULL);

    cin >> n >> m;
    for (int i = 1; i <= n; i++) for (int j = 1; j <= m; j++) cin >> a[i][j];

    fill(par+1, par+n*m+1, -1);

    for (int i = 1; i <= n; i++)
    for (int j = 1; j <= m; j++)
        if (a[i][j] != '.' && !cl[i][j]) bfs(i, j);

    queue<int> q;
    nho[1] = 1;
    q.push(1);
    while (!q.empty()) {
        int u = q.front(); q.pop();
        for (int v : adj[u])
        if (!nho[v]) {
            nho[v] = nho[u]+1;
            q.push(v);
        }
    }
    cout << *max_element(nho + 1, nho + id + 1);



}

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