Submission #3225513

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Source Code Expand

import java.io.IOException; 
import java.io.InputStream; 
import java.io.PrintWriter; 
import java.util.*; 
 

class Main{
	static List<Integer> edges[];

	static int[] leaf;
	static int[] maxpath;
	static int[] secpath;

	static void dfs(int v, int p){
		if(edges[v].size()==1){
			leaf[v]=1;
			maxpath[v]=1;
			return;
		}else if(edges[v].size()==2 && p!=-1){
			int u = edges[v].get(0)+edges[v].get(1)-p;
			dfs(u, v);
			leaf[v]=leaf[u];
			maxpath[v]=maxpath[u]+1;
			return;
		}else{
			for(int u: edges[v])if(u!=p){
				dfs(u, v);
				leaf[v] += leaf[u];
				if(maxpath[u]>maxpath[v]){
					secpath[v]=maxpath[v];
					maxpath[v]=maxpath[u];
				}else if(maxpath[u]>secpath[v]){
					secpath[v]=maxpath[u];
				}
			}
		}
	}
	static int ans=0;
	static void dfs2(int v, int p, int l){
//		out.println(v+" "+leaf[v]+" "+maxpath[v]+" "+secpath[v]);
		if(secpath[v]>0){
			int res = l+leaf[v]+maxpath[v]+secpath[v]-2;
			if(p==-1&&edges[v].size()==2)res++;
			ans=Math.max(ans, res);
		}
		for(int u: edges[v])if(u!=p)dfs2(u, v, l+leaf[v]-leaf[u]);
	}

	static void solve(){
		int n = ni();
		leaf = new int[n];
		maxpath = new int[n];
		secpath = new int[n];
		edges = new List[n];
		for(int i=0;i<n;++i)edges[i]=new ArrayList<>();
		for(int i=0;i<n-1;++i){
			int p=ni()-1, q=ni()-1;
			edges[p].add(q);
			edges[q].add(p);
		}
		int root = 0;
		for(int i=0;i<n;++i)if(edges[i].size()>1)root=i;
		dfs(root, -1);
		dfs2(root, -1, 0);

		out.println(ans);

	} 
 
 
 
 
	 public static void main(String[] args){ 
		 solve(); 
		 out.flush(); 
	 } 
	 private static InputStream in = System.in; 
	 private static PrintWriter out = new PrintWriter(System.out); 
 
	 static boolean inrange(int y, int x, int h, int w){ 
		 return y>=0 && y<h && x>=0 && x<w; 
	 } 
	 @SuppressWarnings("unchecked") 
	 static<T extends Comparable> int lower_bound(List<T> list, T key){ 
		 int lower=-1;int upper=list.size(); 
		 while(upper - lower>1){ 
		 int center =(upper+lower)/2; 
		 if(list.get(center).compareTo(key)>=0)upper=center; 
		 else lower=center; 
		 } 
		 return upper; 
	 } 
	 @SuppressWarnings("unchecked") 
	 static <T extends Comparable> int upper_bound(List<T> list, T key){ 
		 int lower=-1;int upper=list.size(); 
		 while(upper-lower >1){ 
		 int center=(upper+lower)/2; 
		 if(list.get(center).compareTo(key)>0)upper=center; 
		 else lower=center; 
		 } 
		 return upper; 
	 } 
	 @SuppressWarnings("unchecked") 
	 static <T extends Comparable> boolean next_permutation(List<T> list){ 
		 int lastIndex = list.size()-2; 
		 while(lastIndex>=0 && list.get(lastIndex).compareTo(list.get(lastIndex+1))>=0)--lastIndex; 
		 if(lastIndex<0)return false; 
		 int swapIndex = list.size()-1; 
		 while(list.get(lastIndex).compareTo(list.get(swapIndex))>=0)swapIndex--; 
		 T tmp = list.get(lastIndex); 
		 list.set(lastIndex++, list.get(swapIndex)); 
		 list.set(swapIndex, tmp); 
		 swapIndex = list.size()-1; 
		 while(lastIndex<swapIndex){ 
		 tmp = list.get(lastIndex); 
		 list.set(lastIndex, list.get(swapIndex)); 
		 list.set(swapIndex, tmp); 
		 ++lastIndex;--swapIndex; 
		 } 
		 return true; 
	 } 
	 private static final byte[] buffer = new byte[1<<15]; 
	 private static int ptr = 0; 
	 private static int buflen = 0; 
	 private static boolean hasNextByte(){ 
		 if(ptr<buflen)return true; 
		 ptr = 0; 
		 try{ 
			 buflen = in.read(buffer); 
		 } catch (IOException e){ 
			 e.printStackTrace(); 
		 } 
		 return buflen>0; 
	 } 
	 private static int readByte(){ if(hasNextByte()) return buffer[ptr++]; else return -1;} 
	 private static boolean isSpaceChar(int c){ return !(33<=c && c<=126);} 
	 private static int skip(){int res; while((res=readByte())!=-1 && isSpaceChar(res)); return res;} 
 
	 private static double nd(){ return Double.parseDouble(ns()); } 
	 private static char nc(){ return (char)skip(); } 
	 private static String ns(){ 
		 StringBuilder sb = new StringBuilder(); 
		 for(int b=skip();!isSpaceChar(b);b=readByte())sb.append((char)b); 
		 return sb.toString(); 
	 } 
	 private static int[] nia(int n){ 
		 int[] res = new int[n]; 
		 for(int i=0;i<n;++i)res[i]=ni(); 
		 return res; 
	 } 
	 private static long[] nla(int n){ 
		 long[] res = new long[n]; 
		 for(int i=0;i<n;++i)res[i]=nl(); 
		 return res; 
	 } 
	 private static int ni(){ 
		 int res=0,b; 
		 boolean minus=false; 
		 while((b=readByte())!=-1 && !((b>='0'&&b<='9') || b=='-')); 
		 if(b=='-'){ 
			 minus=true; 
			 b=readByte(); 
		 } 
		 for(;'0'<=b&&b<='9';b=readByte())res=res*10+(b-'0'); 
		 return minus ? -res:res; 
	 } 
	 private static long nl(){ 
		 long res=0,b; 
		 boolean minus=false; 
		 while((b=readByte())!=-1 && !((b>='0'&&b<='9') || b=='-')); 
		 if(b=='-'){ 
			 minus=true; 
			 b=readByte(); 
		 } 
		 for(;'0'<=b&&b<='9';b=readByte())res=res*10+(b-'0'); 
		 return minus ? -res:res; 
	} 
} 

Submission Info

Compile Error

Note: ./Main.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.

Judge Result