File size: 3,964 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 | #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), pos(n + 1);
for (int i = 1; i <= n; ++i) {
cin >> p[i];
}
vector<vector<pair<int,int>>> adj(n + 1);
vector<pair<int,int>> edges(n);
for (int i = 1; i <= n - 1; ++i) {
int u, v;
cin >> u >> v;
edges[i] = {u, v};
adj[u].push_back({v, i});
adj[v].push_back({u, i});
}
for (int i = 1; i <= n; ++i) pos[p[i]] = i;
vector<int> deg(n + 1, 0);
for (int i = 1; i <= n; ++i) deg[i] = (int)adj[i].size();
vector<char> alive(n + 1, 1);
int alive_count = n;
deque<int> leaves;
for (int i = 1; i <= n; ++i) if (deg[i] == 1) leaves.push_back(i);
vector<int> ops;
vector<int> parent(n + 1), pedge(n + 1);
while (alive_count > 0) {
int v = -1;
while (!leaves.empty()) {
int t = leaves.front(); leaves.pop_front();
if (alive[t] && deg[t] == 1) { v = t; break; }
}
if (v == -1) {
if (alive_count == 1) {
int last = -1;
for (int i = 1; i <= n; ++i) if (alive[i]) { last = i; break; }
alive[last] = 0;
--alive_count;
break;
} else {
// Should not happen in a tree; fallback: find any alive leaf (deg==1) by scan
for (int i = 1; i <= n; ++i) {
if (alive[i] && deg[i] == 1) { v = i; break; }
}
if (v == -1) {
// If still none, break to avoid infinite loop (theoretically impossible)
break;
}
}
}
int s = pos[v];
if (s != v) {
fill(parent.begin(), parent.end(), -1);
fill(pedge.begin(), pedge.end(), -1);
deque<int> q;
parent[s] = s;
q.push_back(s);
while (!q.empty() && parent[v] == -1) {
int x = q.front(); q.pop_front();
for (auto &pr : adj[x]) {
int y = pr.first, e = pr.second;
if (!alive[y]) continue;
if (parent[y] != -1) continue;
parent[y] = x;
pedge[y] = e;
q.push_back(y);
if (y == v) break;
}
}
vector<int> path_nodes;
int cur = v;
path_nodes.push_back(v);
while (cur != s) {
cur = parent[cur];
path_nodes.push_back(cur);
}
reverse(path_nodes.begin(), path_nodes.end());
for (size_t i = 0; i + 1 < path_nodes.size(); ++i) {
int a = path_nodes[i];
int b = path_nodes[i + 1];
int e = pedge[b];
int x = p[a], y = p[b];
p[a] = y; p[b] = x;
pos[x] = b; pos[y] = a;
ops.push_back(e);
}
}
alive[v] = 0;
--alive_count;
for (auto &pr : adj[v]) {
int to = pr.first;
if (alive[to]) {
--deg[to];
if (deg[to] == 1) leaves.push_back(to);
}
}
deg[v] = 0;
}
cout << ops.size() << '\n';
for (int e : ops) {
cout << 1 << ' ' << e << '\n';
}
}
return 0;
} |