package yukicoder; import java.util.ArrayList; import java.util.Arrays; import java.util.HashSet; import java.util.Iterator; import java.util.Scanner; import java.util.Set; public class Main { public static void main(String[] args) { long S=System.currentTimeMillis(); new Main().solver(); long T=System.currentTimeMillis(); System.err.println((T-S)+"ms"); } void solver() { Scanner sc = new Scanner(System.in); long S = sc.nextLong(); Graph g = set_edge(S); Pair p=ms(g); System.out.println((p.cardinality+1)); boolean f=false; for(int i=0;i= P) { g.set_edge(i, j); } } } return g; } // 無向グラフ class Graph { ArrayList[] e; int n; int[] deg; boolean[] valid_vertices;//選ぶことのできる頂点 boolean[] choosed_vertices;//選ばれた頂点 Graph(int n) { this.n = n; deg = new int[n]; valid_vertices = new boolean[n]; choosed_vertices=new boolean[n]; Arrays.fill(valid_vertices, true); e = new ArrayList[n]; for (int i = 0; i < n; i++) { e[i] = new ArrayList<>(); } } // 無向グラフの辺a<->を作成 void set_edge(int a, int b) { if(!e[a].contains((Integer)b)){ e[a].add(b); e[b].add(a); deg[a]++; deg[b]++; } } // 辺a<->bを消去 void delete_undirected_edge(int a, int b) { e[a].remove((Integer) b); e[b].remove((Integer) a); deg[a]--; deg[b]--; } // 頂点vを消去 void delete_vertice(int v) { while (e[v].size() > 0) { int u = e[v].get(0); delete_undirected_edge(u, v); } valid_vertices[v] = false; } // 頂点vと、vの隣接頂点を消去 void delete_v_with_neighbours(int v) { while (e[v].size() > 0) { int u = e[v].get(0); delete_vertice(u); } delete_vertice(v); } // deep copy Graph copy() { Graph g = new Graph(this.n); for (int i = 0; i < n; i++) { g.deg[i] = deg[i]; } for (int i = 0; i < n; i++) { g.valid_vertices[i] = valid_vertices[i]; } for (int i = 0; i < n; i++) { for (int j = 0; j < e[i].size(); j++) { (g.e[i]).add(e[i].get(j)); } } return g; } } Pair ms(Graph g) { int[] deg = g.deg; ArrayList[] e = g.e; boolean[] valid_vertices = g.valid_vertices; int n = g.n; int A = -1;// 最も次数の小さい頂点 int B = -1;// Aにつながる頂点のうち最も次数の大きいもの int deg_me_min = Integer.MAX_VALUE / 4; int deg_to_max = -Integer.MAX_VALUE / 4; for (int i = 0; i < n; i++) { if (!valid_vertices[i]) continue; if (deg[i] < deg_me_min) { A = i; deg_me_min = deg[i]; if (deg_me_min <= 1) { g.delete_v_with_neighbours(i); Pair p= ms(g); p.choosed_vertices[i]=true; p.cardinality++; return p; } deg_to_max = deg[e[A].get(0)]; B = e[A].get(0); for (int j = 0; j < e[A].size(); j++) { int u = e[A].get(j); if (!valid_vertices[u]) continue; if (deg[u] > deg_to_max) { B = u; deg_to_max = deg[u]; } } } else if (deg[i] == deg_me_min) { for (int j = 0; j < e[A].size(); j++) { int u = e[A].get(j); if (!valid_vertices[u]) continue; if (deg[u] > deg_to_max) { B = u; A = i; deg_to_max = deg[u]; } } } } if (A == -1 && B == -1) return new Pair(0,new boolean[n]); if(dominance(A,B,g)){ g.delete_vertice(A); } Graph g2 = g.copy(); g2.delete_v_with_neighbours(B); g.delete_vertice(B); Pair p1=ms(g); Pair p2=ms(g2); p2.cardinality++; p2.choosed_vertices[B]=true; if(p1.cardinality>p2.cardinality){ return p1; }else{ return p2; } // } } class Pair{ int cardinality; boolean[] choosed_vertices; Pair(int cardinality,boolean[] choosed_vertices){ this.cardinality=cardinality; this.choosed_vertices=choosed_vertices; } } //whethere N(B)&B is subset of N(A)&A or not; boolean dominance(int A,int B,Graph g){ Set as=new HashSet<>(); Set bs=new HashSet<>(); ArrayList[] e=g.e; for(int i=0;i it=bs.iterator();it.hasNext();){ if(!as.contains(it.next())){ return false; } } return true; } }