import java.io.FileReader; import java.io.IOException; import java.util.*; import java.util.function.Consumer; public class clique2_ablations_streamsafe { static int n, m; public static List main(String[] args) throws Exception { if (args.length < 2) { System.err.println("Usage: java clique2_ablations "); } final double EPS = Double.parseDouble(args[0]); Scanner r; try { r = new Scanner(new FileReader(args[1])); } catch (IOException e) { System.err.println("Could not open " + args[1] + ". Falling back to stdin."); r = new Scanner(System.in); } n = r.nextInt(); m = r.nextInt(); @SuppressWarnings("unchecked") List[] adj = new ArrayList[n + 1]; for (int i = 1; i <= n; i++) adj[i] = new ArrayList<>(); for (int i = 0; i < m; i++) { int a = r.nextInt(), b = r.nextInt(); adj[a].add(b); adj[b].add(a); } r.close(); long t0 = System.nanoTime(); List res = runLaplacianRMC(adj); // <- optimized O(Mk) long t1 = System.nanoTime(); // System.out.printf(Locale.US, "%.6f, %d%n", res.bestSL, res.bestRoot); System.out.printf(Locale.US, "Runtime: %.3f ms%n", (t1 - t0) / 1_000_000.0); return res; } public static List runLaplacianRMC(List[] adj1Based) { ArrayList out = new ArrayList<>(); runLaplacianRMCStreaming(adj1Based, out::add); return out; } /** * Optimized O(Mk) algorithm using reverse-peeling orientation + pred_sum pushes. */ public static List runLaplacianRMCStreaming(List[] adj, Consumer sink) { final int n = adj.length - 1; // infer n from 1-based adjacency // Phase 1: peeling (same as before) int[] deg0 = new int[n + 1]; PriorityQueue pq = new PriorityQueue<>(); for (int i = 1; i <= n; i++) { deg0[i] = adj[i].size(); pq.add(new Pair(i, deg0[i])); } Deque peelStack = new ArrayDeque<>(n); // store nodes only while (!pq.isEmpty()) { Pair p = pq.poll(); if (p.degree != deg0[p.node]) continue; // stale peelStack.push(p.node); for (int v : adj[p.node]) { if (deg0[v] > 0) { deg0[v]--; pq.add(new Pair(v, deg0[v])); } } deg0[p.node] = 0; } // Build addition order and index int[] addOrder = new int[n]; int[] idx = new int[n + 1]; for (int t = 0; t < n; t++) { int u = peelStack.pop(); // reverse-peeling (addition order) addOrder[t] = u; idx[u] = t; } // Phase 1.5: orient edges by idx and sort successors @SuppressWarnings("unchecked") ArrayList[] succ = new ArrayList[n + 1]; @SuppressWarnings("unchecked") ArrayList[] pred = new ArrayList[n + 1]; for (int i = 1; i <= n; i++) { succ[i] = new ArrayList<>(); pred[i] = new ArrayList<>(); } for (int u = 1; u <= n; u++) { for (int v : adj[u]) { if (u < v) { // handle undirected edge once if (idx[u] < idx[v]) { succ[u].add(v); pred[v].add(u); } else { succ[v].add(u); pred[u].add(v); } } } } for (int v = 1; v <= n; v++) { if (succ[v].size() > 1) { succ[v].sort(Comparator.comparingInt(w -> idx[w])); } // pred[v] need not be sorted } // Phase 2: reverse reconstruction with O(k) per edge DSU dsu = new DSU(n); // tracks parent, size, and Q (double) int[] deg = new int[n + 1]; // current degree long[] predSum = new long[n + 1]; // sum of degrees of predecessors double bestSL = 0.0; int bestRoot = 0; // helper: sum of degrees of active successors of v whose idx < T final SumSucc sumSucc = new SumSucc(succ, idx, deg); @SuppressWarnings("unchecked") HashSet[] compNodes = new HashSet[n + 1]; for (int i = 1; i <= n; i++) compNodes[i] = new HashSet<>(); List recon = new ArrayList<>(); for (int u : addOrder) { dsu.makeIfNeeded(u); // create singleton component // Single-node score (Q=0) long Su = 0L; // running sum over degrees of neighbors already attached to u final int Tu = idx[u]; compNodes[u].add(u); // connect u to all its predecessors (earlier neighbors) for (int v : pred[u]) { long a = deg[u]; long b = deg[v]; // S_v = pred_sum[v] + sum of deg[w] for successors w of v with idx[w] < idx[u] long Sv = predSum[v] + sumSucc.until(v, Tu); long dQu = 2L * a * a - 2L * Su + a; long dQv = 2L * b * b - 2L * Sv + b; long edgeTerm = (a - b) * (a - b); int ru = dsu.find(u); int rv = dsu.find(v); dsu.Q[ru] += (double) dQu; dsu.Q[rv] += (double) dQv; int r; if (ru != rv) { r = dsu.union(ru, rv); dsu.Q[r] += (double) edgeTerm; int o = (r == ru) ? rv : ru; compNodes[r].addAll(compNodes[o]); compNodes[o].clear(); } else { r = ru; dsu.Q[r] += (double) edgeTerm; } // degree increments deg[u] += 1; deg[v] += 1; // Update sumDeg for the component - THIS WAS MISSING dsu.sumDeg[r] += 2; // push +1 to predSum of successors (outdegree ≤ k) for (int y : succ[u]) predSum[y] += 1; for (int y : succ[v]) predSum[y] += 1; // maintain Su: add deg[v] AFTER its increment Su += deg[v]; } int r = dsu.find(u); int[] nodes = compNodes[r].stream().mapToInt(x -> x-1).toArray(); Arrays.sort(nodes); int compId = dsu.componentId(r); SnapshotDTO snap = new SnapshotDTO(compId, nodes, nodes.length, dsu.sumDeg[r], dsu.Q[r]); sink.accept(snap); } return recon; } // Small helper for successor-degree partial sums static final class SumSucc { final ArrayList[] succ; final int[] idx; final int[] deg; SumSucc(ArrayList[] succ, int[] idx, int[] deg) { this.succ = succ; this.idx = idx; this.deg = deg; } /** Sum of deg[w] over successors w of v with idx[w] < T (succ[v] sorted by idx). */ long until(int v, int T) { long s = 0L; final ArrayList sv = succ[v]; final int sz = sv.size(); for (int i = 0; i < sz; i++) { int w = sv.get(i); if (idx[w] >= T) break; s += deg[w]; } return s; } } // Helpers static class Result { double bestSL; int bestRoot; } static class Pair implements Comparable { final int node, degree; Pair(int node, int degree) { this.node = node; this.degree = degree; } public int compareTo(Pair o) { if (degree != o.degree) return Integer.compare(degree, o.degree); return Integer.compare(node, o.node); } } /** DSU that also tracks component Laplacian Q as double. */ static class DSU { final int[] parent; final int[] size; final boolean[] made; final double[] Q; final int[] sumDeg; final int[] compId; // compId[root] > 0 iff the root represents a live component int nextCompId = 1; // 1-based; 0 means "unassigned" DSU(int n) { parent = new int[n + 1]; size = new int[n + 1]; made = new boolean[n + 1]; Q = new double[n + 1]; sumDeg = new int[n + 1]; compId = new int[n + 1]; } void makeIfNeeded(int v) { if (!made[v]) { made[v] = true; parent[v] = v; size[v] = 1; Q[v] = 0.0; sumDeg[v] = 0; if (compId[v] == 0) compId[v] = nextCompId++; } } int find(int v) { if (!made[v]) return v; // treat as isolated until made if (parent[v] != v) parent[v] = find(parent[v]); return parent[v]; } int union(int a, int b) { makeIfNeeded(a); makeIfNeeded(b); int ra = find(a), rb = find(b); if (ra == rb) return ra; if (size[ra] < size[rb]) { int t = ra; ra = rb; rb = t; } parent[rb] = ra; size[ra] += size[rb]; Q[ra] += Q[rb]; sumDeg[ra] += sumDeg[rb]; int aId = compId[ra], bId = compId[rb]; int keep = (aId == 0) ? bId : (bId == 0 ? aId : Math.min(aId, bId)); compId[ra] = keep; compId[rb] = 0; // retire loser id return ra; } int componentId(int v) { return compId[find(v)]; } } public static final class SnapshotDTO { public final int componentId; public final int[] nodes; // 0-based ids in the original graph public final int nC; public final long sumDegIn; // sum of internal degrees at this snapshot public final double Q; // d^T L_C d at this snapshot public SnapshotDTO(int componentId, int[] nodes, int nC, long sumDegIn, double Q) { this.componentId = componentId; this.nodes = nodes; this.nC = nC; this.sumDegIn = sumDegIn; this.Q = Q; } } }