POJ1113凸包

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import java.io.BufferedReader;import java.io.IOException;import java.io.InputStream;import java.io.InputStreamReader;import java.io.PrintWriter;import java.io.StreamTokenizer;import java.math.BigInteger;import java.util.ArrayList;import java.util.Arrays;import java.util.Collections;import java.util.Comparator;import java.util.Scanner;import java.util.Stack;import java.util.StringTokenizer;public class Main{        public static void main(String[] args) throws IOException{                InputReader in = new InputReader(System.in) ;                StreamTokenizer cin = new StreamTokenizer(new BufferedReader(new InputStreamReader(System.in)));                PrintWriter out = new PrintWriter(System.out);                int n = in.nextInt()  , r  = in.nextInt() ;                P[] p = new P[n] ;                for(int i = 0 ; i < n ; i++) p[i] = new P(in.nextInt() , in.nextInt()) ;                out.printf("%.0f", new Task().solve(p , r) )  ;                out.flush() ;        }}class  Task{       public double solve(P[] p , int r){              double  res = 0 ;               P[] qs = convexHull(p) ;              for(int i = 0 , n = qs.length ; i < n ; i++){                   res += qs[i].dist(qs[(i + 1) % n]) ;              }              res += 2.0 * Math.PI * r ;              return res ;       }         public P[] convexHull(P[] ps){              int n = ps.length , k = 0 ;              if(n <= 0) return ps ;              Arrays.sort(ps , new Psort()) ;               P[] qs = new P[n+2] ;              for(int i = 0 ; i < n ; i++){                  while(k > 1 && qs[k-1].sub(qs[k-2]).det(ps[i].sub(qs[k-1])) <= 0) k-- ;                  qs[k++] = ps[i] ;              }              for(int i = n - 2 , t = k ; i >= 0 ; i--){                  while(k > t && qs[k-1].sub(qs[k-2]).det(ps[i].sub(qs[k-1])) <= 0) k-- ;                  qs[k++] = ps[i] ;              }              P[] res = new P[k-1] ;              System.arraycopy(qs , 0 , res , 0 , k-1) ;              return res ;       } }class P{      int x , y ;      public P(){      }      public P(int x , int y){             this.x = x ;             this.y = y ;      }      public P sub(P o){             return new P(x - o.x , y - o.y) ;      }      public double dot(P o){             return x * o.x + y * o.y ;      }      public double det(P o){             return x * o.y - y * o.x ;      }      public double  dist(P o){             return  Math.sqrt( Math.pow(x - o.x, 2) + Math.pow(y - o.y, 2) ) ;      }}class Psort implements Comparator<P>{      public int compare(P o1, P o2) {             if(o1.x != o2.x) return o1.x - o2.x ;              return o1.y - o2.y ;      } }class InputReader {    public BufferedReader reader;    public StringTokenizer tokenizer;    public InputReader(InputStream stream) {        reader = new BufferedReader(new InputStreamReader(stream), 32768);        tokenizer = null;    }    public String next() {        while (tokenizer == null || !tokenizer.hasMoreTokens()) {            try {                tokenizer = new StringTokenizer(reader.readLine());            } catch (IOException e) {                throw new RuntimeException(e);            }        }        return tokenizer.nextToken();    }    public int nextInt() {        return Integer.parseInt(next());    }}
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