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1
8 package org.lsmp.djep.xjep;
9 import java.util.*;
10
14 public class XMath {
15
16 static class LongPair {
17 long a,b;
18 public LongPair(long x,long y) { a=x; b=y;}
19 long x() { return a; }
20 long y() { return b; }
21 public boolean equals(Object  o) {
22 if(!( o instanceof LongPair)) return false;
23 LongPair p = (LongPair) o;
24 return (a == p.a) && (b == p.b);
25 }
26
27 public int hashCode() {
28 int result = 17;
29 int xi = (int)(a^(a>>32));
30 int yi = (int)(b^(b>>32));
31 result = 37*result+xi;
32 result = 37*result+yi;
33 return result;
34 }
35 public String toString() { return "("+a+","+b+")"; }
36
37 }
38 static Hashtable pascal = new Hashtable();
39
40 public static long binomial(long n,long i)
41 {
42 if(i==0 || n==i) return 1;
43 if(i==1 || n==i-1 ) return n;
44 return binomial(new LongPair(n,i));
45 }
46
47 public static long binomial(LongPair pair)
48 {
49 Object find = pascal.get(pair);
50 if(find == null)
51 {
52 long l = binomial(pair.x()-1,pair.y()-1);
53 long r = binomial(pair.x()-1,pair.y());
54 pascal.put(pair,new Long (l+r));
55 return l+r;
56 }
57 else return ((Long ) find).longValue();
58 }
59 }
60 |
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