File size: 3,718 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 | #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), val(n + 1), pos(n + 1);
for (int i = 1; i <= n; ++i) {
cin >> p[i];
val[i] = p[i];
pos[p[i]] = i;
}
vector<pair<int,int>> edges(n); // 1..n-1 used
vector<vector<pair<int,int>>> adj(n + 1);
vector<int> deg(n + 1, 0), degActive(n + 1, 0);
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});
deg[u]++; deg[v]++;
}
degActive = deg;
vector<char> removed(n + 1, 0);
int activeCnt = n;
queue<int> q;
for (int i = 1; i <= n; ++i) if (degActive[i] <= 1) q.push(i);
vector<int> opsEdges;
while (activeCnt > 1) {
int u = -1;
while (!q.empty()) {
int x = q.front(); q.pop();
if (!removed[x] && degActive[x] == 1) { u = x; break; }
}
if (u == -1) {
for (int i = 1; i <= n; ++i) {
if (!removed[i] && degActive[i] == 1) { u = i; break; }
}
}
if (u == -1) break; // should not happen in a tree
if (val[u] != u) {
int start = pos[u];
if (start != u) {
vector<int> parent(n + 1, -1);
vector<int> pEdge(n + 1, -1);
queue<int> qb;
qb.push(start);
parent[start] = start;
while (!qb.empty() && parent[u] == -1) {
int x = qb.front(); qb.pop();
for (auto [y, ei] : adj[x]) {
if (removed[y]) continue;
if (parent[y] != -1) continue;
parent[y] = x;
pEdge[y] = ei;
qb.push(y);
}
}
// reconstruct path vertices from start to u
vector<int> pathVrev;
int cur = u;
while (true) {
pathVrev.push_back(cur);
if (cur == start) break;
cur = parent[cur];
}
vector<int> pathV(pathVrev.rbegin(), pathVrev.rend());
for (size_t t = 0; t + 1 < pathV.size(); ++t) {
int a = pathV[t], b = pathV[t + 1];
int eindex = pEdge[b]; // parent[b] == a
int tokenA = val[a], tokenB = val[b];
swap(val[a], val[b]);
pos[tokenA] = b;
pos[tokenB] = a;
opsEdges.push_back(eindex);
}
}
}
// remove u
removed[u] = 1;
activeCnt--;
int neighbor = -1, cnt = 0;
for (auto [v, ei] : adj[u]) {
if (!removed[v]) { neighbor = v; cnt++; }
}
if (cnt == 1) {
degActive[neighbor]--;
if (degActive[neighbor] == 1) q.push(neighbor);
}
degActive[u] = 0;
}
cout << (int)opsEdges.size() << '\n';
for (int e : opsEdges) {
cout << 1 << ' ' << e << '\n';
}
}
return 0;
} |