File size: 4,583 Bytes
1fd0050
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
#include <bits/stdc++.h>
using namespace std;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    
    int T;
    cin >> T;
    for (int t = 0; t < T; ++t) {
        int n;
        cin >> n;
        vector<int> p(n + 1);
        for (int i = 1; i <= n; ++i) {
            cin >> p[i];
        }
        vector<pair<int, int>> edge_list(n);
        vector<vector<pair<int, int>>> edge_adj(n + 1);
        for (int i = 1; i <= n - 1; ++i) {
            int u, v;
            cin >> u >> v;
            edge_list[i] = {u, v};
            edge_adj[u].emplace_back(v, i);
            edge_adj[v].emplace_back(u, i);
        }
        // Build tree_adj for dist
        vector<vector<int>> tree_adj(n + 1);
        for (int i = 1; i <= n - 1; ++i) {
            int u = edge_list[i].first, v = edge_list[i].second;
            tree_adj[u].push_back(v);
            tree_adj[v].push_back(u);
        }
        // Precompute all pairs dist
        vector<vector<int>> dist(n + 1, vector<int>(n + 1, -1));
        for (int s = 1; s <= n; ++s) {
            vector<int> d(n + 1, -1);
            d[s] = 0;
            queue<int> q;
            q.push(s);
            while (!q.empty()) {
                int u = q.front();
                q.pop();
                for (int v : tree_adj[u]) {
                    if (d[v] == -1) {
                        d[v] = d[u] + 1;
                        q.push(v);
                    }
                }
            }
            for (int i = 1; i <= n; ++i) {
                dist[s][i] = d[i];
            }
        }
        // Current label
        vector<int> label = p;
        // Operations
        vector<vector<int>> operations;
        bool is_sorted = false;
        while (!is_sorted) {
            bool check_sorted = true;
            for (int i = 1; i <= n; ++i) {
                if (label[i] != i) {
                    check_sorted = false;
                    break;
                }
            }
            is_sorted = check_sorted;
            if (is_sorted) break;
            // Collect prio and norm
            vector<int> prio, norm;
            for (int eid = 1; eid <= n - 1; ++eid) {
                int u = edge_list[eid].first;
                int v = edge_list[eid].second;
                int lu = label[u], lv = label[v];
                int tu = lu, tv = lv;
                int old_du = dist[u][tu];
                int new_du = dist[v][tu];
                int d1 = new_du - old_du;
                int old_dv = dist[v][tv];
                int new_dv = dist[u][tv];
                int d2 = new_dv - old_dv;
                int del = d1 + d2;
                if (del <= 0) {
                    if (del == -2) {
                        prio.push_back(eid);
                    } else { // del == 0
                        bool can = false;
                        if (d1 == 1) {
                            if (old_du == 0) can = true;
                        } else if (d2 == 1) {
                            if (old_dv == 0) can = true;
                        }
                        if (can) {
                            norm.push_back(eid);
                        }
                    }
                }
            }
            // Build selected
            vector<int> selected;
            vector<bool> used(n + 1, false);
            auto add_if_possible = [&](int eid) -> bool {
                int u = edge_list[eid].first;
                int v = edge_list[eid].second;
                if (!used[u] && !used[v]) {
                    selected.push_back(eid);
                    used[u] = true;
                    used[v] = true;
                    return true;
                }
                return false;
            };
            for (int eid : prio) {
                add_if_possible(eid);
            }
            for (int eid : norm) {
                add_if_possible(eid);
            }
            if (selected.empty()) {
                // Should not happen
                break;
            }
            // Record
            operations.push_back(selected);
            // Perform swaps
            for (int eid : selected) {
                int u = edge_list[eid].first;
                int v = edge_list[eid].second;
                swap(label[u], label[v]);
            }
        }
        // Output
        cout << operations.size() << '\n';
        for (auto& op : operations) {
            cout << op.size();
            for (int e : op) {
                cout << " " << e;
            }
            cout << '\n';
        }
    }
    return 0;
}