lessons/参考实现/09-基环树/CodeForces-1270G.cpp

#include <bits/stdc++.h>
using namespace std;

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

    int tests;
    cin >> tests;
    while (tests--) {
        int n;
        cin >> n;
        vector<int> next(n), indegree(n, 0);
        for (int i = 0; i < n; ++i) {
            int value;
            cin >> value;
            next[i] = i - value;
            ++indegree[next[i]];
        }
        queue<int> leaves;
        for (int i = 0; i < n; ++i) if (indegree[i] == 0) leaves.push(i);
        while (!leaves.empty()) {
            int v = leaves.front();
            leaves.pop();
            if (--indegree[next[v]] == 0) leaves.push(next[v]);
        }
        int start = 0;
        while (indegree[start] == 0) ++start;
        vector<int> cycle;
        int v = start;
        do {
            cycle.push_back(v);
            v = next[v];
        } while (v != start);
        cout << cycle.size() << '\n';
        for (int x : cycle) cout << x + 1 << ' ';
        cout << '\n';
    }
    return 0;
}