File size: 2,808 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 | #include <bits/stdc++.h>
using namespace std;
int main() {
ios::sync_with_stdio(false);
cin.tie(nullptr);
int T;
if (!(cin >> T)) return 0;
while (T--) {
int n;
cin >> n;
vector<int> p(n + 1);
for (int i = 1; i <= n; ++i) cin >> p[i];
vector<vector<pair<int,int>>> adj(n + 1);
for (int i = 1; i <= n - 1; ++i) {
int u, v;
cin >> u >> v;
adj[u].push_back({v, i});
adj[v].push_back({u, i});
}
// Decompose permutation p into transpositions
vector<pair<int,int>> trans;
vector<char> vis(n + 1, 0);
for (int i = 1; i <= n; ++i) {
if (!vis[i]) {
int cur = i;
vector<int> cyc;
while (!vis[cur]) {
vis[cur] = 1;
cyc.push_back(cur);
cur = p[cur];
}
int L = (int)cyc.size();
if (L > 1) {
for (int t = 1; t < L; ++t) {
trans.push_back({cyc[0], cyc[t]});
}
}
}
}
vector<int> ops;
ops.reserve(2 * n * n);
if (!trans.empty()) {
vector<int> parent(n + 1), parentEdge(n + 1), q(n + 1);
for (auto [u_orig, v_orig] : trans) {
int u = u_orig, v = v_orig;
// BFS to find path from u to v
for (int i = 1; i <= n; ++i) parent[i] = -1;
int head = 0, tail = 0;
q[tail++] = u;
parent[u] = 0;
parentEdge[u] = 0;
while (head < tail) {
int x = q[head++];
if (x == v) break;
for (auto [to, idx] : adj[x]) {
if (parent[to] == -1) {
parent[to] = x;
parentEdge[to] = idx;
q[tail++] = to;
}
}
}
vector<int> path;
int cur = v;
while (cur != u) {
path.push_back(parentEdge[cur]);
cur = parent[cur];
}
reverse(path.begin(), path.end());
int L = (int)path.size();
// Forward along path
for (int e : path) ops.push_back(e);
// Backward along path except last edge
for (int i = L - 2; i >= 0; --i) ops.push_back(path[i]);
}
}
int m = (int)ops.size();
cout << m << '\n';
for (int e : ops) {
cout << 1 << ' ' << e << '\n';
}
}
return 0;
} |