[Toph] D. Mushroom Kingdom

 

Problem Link    : D. Mushroom Kingdom
Category        : Bitmask, Bfs
Contest         : Intra AIUB Programming Contest 2024 (Senior)

#include "bits/stdc++.h"
using namespace std;
#define int     long long int
#define endl    '\n'
 
using pii = pair<int, int>;
 
int dr[] = {1, -1, 0, 0}; // 4 Direction
int dc[] = {0, 0, 1, -1};
 
void task() {
    int n;
    cin >> n;
    vector<char> chars;
    vector<vector<char>> grid(n + 1, vector<char>(n + 1));
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= n; j++) {
            cin >> grid[i][j];
            chars.push_back(grid[i][j]);
        }
    }
    pii src;
    cin >> src.first >> src.second;
    pii des;
    cin >> des.first >> des.second;
    sort(chars.begin(), chars.end());
    chars.erase(unique(chars.begin(), chars.end()), chars.end());
    int ans = 10;
    for (int mask = 0; mask < (1 << (int)chars.size()); mask++) {
        set<int> validChars;
        for (int i = 0; i < chars.size(); i++) {
            if (mask >> i & 1) {
                validChars.insert(chars[i]);
            }
        }
        vector<vector<bool>> visited(n + 1, vector<bool>(n + 1));
        queue<pii> pq;
        if (validChars.count(grid[src.first][src.second])) {
            pq.push(src);
            visited[src.first][src.second] = 1;
        }
        while (pq.size()) {
            pii cur = pq.front(); pq.pop();
            for (int k = 0; k < 4; k++) {
                int x = cur.first + dr[k];
                int y = cur.second + dc[k];
                if (x >= 1 and x <= n and y >= 1 and y <= n and visited[x][y] == 0 and validChars.count(grid[x][y])) {
                    pq.push(pii(x, y));
                    visited[x][y] = 1;
                }
            }
        }
        if (visited[des.first][des.second]) {
            ans = min(ans, (int)__builtin_popcount(mask));
        }
    }
    cout << ans << endl;
}
 
signed main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr); cout.tie(nullptr);
    cout.precision(12);
 
    bool FILEIO = true; string FILE = "in.txt";
    if (FILEIO and fopen(FILE.c_str(), "r")) {
        freopen(FILE.c_str(), "r", stdin);
    }
 
    int tc;
    cin >> tc;
    for (int tcase = 1; tcase <= tc; tcase++) {
        task();
    }
}