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added methods to handle BIG combinations #40

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added methods to handle BIG combinations #40

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23 changes: 21 additions & 2 deletions java-combinations/Combination.java
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Original file line number Diff line number Diff line change
Expand Up @@ -6,7 +6,7 @@ public class Combination {


public static void main(String[] args){
Object[] elements = new Object[] {'A','B','C','D','E', 'F', 'G', 'H'};
Object[] elements = new Object[] {'A','B','C','D','E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'};

combination(elements,7);
}
Expand All @@ -24,7 +24,7 @@ public static void combination(Object[] elements, int K){
}
// calculate the possible combinations
// e.g. c(4,2)
c(N,K);
bigC(N,K);

// get the combination by index
// e.g. 01 --> AB , 23 --> CD
Expand Down Expand Up @@ -82,6 +82,18 @@ public static int c(int n, int r){
return ncr;
}

public static BigInteger bigC(int n, int r){
BigInteger nf=bigFact(n);
BigInteger rf=bigFact(r);
BigInteger nrf=bigFact(n-r);
BigInteger npr=nf.divide(nrf);
BigInteger ncr=npr.divide(rf);

System.out.println("C("+n+","+r+") = "+ ncr);

return ncr;
}

public static int fact(int n)
{
if(n == 0)
Expand All @@ -90,6 +102,13 @@ public static int fact(int n)
return n * fact(n-1);
}

public static BigInteger bigFact(int n) {
if(n== 0)
return BigInteger.valueOf(1);
else
return BigInteger.valueOf(n).multiply(bigFact(n-1));

}

public static void print(int[] combination, Object[] elements){

Expand Down