Solution.java

class Solution {
    public int collectTheCoins(int[] coins, int[][] edges) {
        int n = coins.length;
        Set<Integer>[] g = new Set[n];
        Arrays.setAll(g, k -> new HashSet<>());
        for (var e : edges) {
            int a = e[0], b = e[1];
            g[a].add(b);
            g[b].add(a);
        }
        Deque<Integer> q = new ArrayDeque<>();
        for (int i = 0; i < n; ++i) {
            if (coins[i] == 0 && g[i].size() == 1) {
                q.offer(i);
            }
        }
        while (!q.isEmpty()) {
            int i = q.poll();
            for (int j : g[i]) {
                g[j].remove(i);
                if (coins[j] == 0 && g[j].size() == 1) {
                    q.offer(j);
                }
            }
            g[i].clear();
        }
        q.clear();
        for (int k = 0; k < 2; ++k) {
            for (int i = 0; i < n; ++i) {
                if (g[i].size() == 1) {
                    q.offer(i);
                }
            }
            for (int i : q) {
                for (int j : g[i]) {
                    g[j].remove(i);
                }
                g[i].clear();
            }
        }
        int ans = 0;
        for (var e : edges) {
            int a = e[0], b = e[1];
            if (g[a].size() > 0 && g[b].size() > 0) {
                ans += 2;
            }
        }
        return ans;
    }
}