[UVa] 10303 - How Many Trees?

題目網址: https://goo.gl/Fhbzhn

題意:
(from luckycat)


解法:
大數 & 卡塔蘭數。

TAG: Catalan Number, Math, BigNum

注意:

程式碼:

	/**
	* Tittle: 10303 - How Many Trees?
	* Author: Cheng-Shih, Wong
	* Date: 2015/06/11
	*/
	import java.util.*;
	import java.math.*;
	public class Main {
	public static void main( String[] args ) {
	final int N = 1005;
	BigInteger[] cat = new BigInteger[N];
	Scanner input = new Scanner(System.in);
	int n;
	// init
	cat[1] = BigInteger.ONE;
	for( int i=1; i<1000; ++i )
	cat[i+1] = cat[i].multiply( BigInteger.valueOf(2*(2*i+1)) ).divide( BigInteger.valueOf(i+2) );
	// solve
	while( input.hasNext() ) {
	n = input.nextInt();
	System.out.println(cat[n]);
	}
	input.close();
	}
	}

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