Solution2.cpp

class Solution {
public:
    int n;

    int shortestPathLength(vector<vector<int>>& graph) {
        n = graph.size();
        priority_queue<tuple<int, int, int>, vector<tuple<int, int, int>>, greater<tuple<int, int, int>>> q;
        vector<vector<int>> dist(n, vector<int>(1 << n, INT_MAX));
        for (int i = 0; i < n; ++i) {
            q.push({f(1 << i), i, 1 << i});
            dist[i][1 << i] = 0;
        }
        while (!q.empty()) {
            auto [_, u, state] = q.top();
            q.pop();
            if (state == (1 << n) - 1) return dist[u][state];
            for (int v : graph[u]) {
                int nxt = state | (1 << v);
                if (dist[v][nxt] > dist[u][state] + 1) {
                    dist[v][nxt] = dist[u][state] + 1;
                    q.push({dist[v][nxt] + f(nxt), v, nxt});
                }
            }
        }
        return 0;
    }

    int f(int state) {
        int ans = 0;
        for (int i = 0; i < n; ++i)
            if (((state >> i) & 1) == 0)
                ++ans;
        return ans;
    }
};