factorial.java

来自「a molecular graph kernel based on iterat」· Java 代码 · 共 110 行

/**
 * ISOAK - Iterative similarity optimal assignment kernel.
 * 
 * Written by Matthias Rupp 2006-2007.
 * Copyright (c) 2006-2007, Matthias Rupp, Ewgenij Proschak, Gisbert Schneider.
 * 
 * All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 * 
 *  * The above copyright notice, this permission notice and the following disclaimers
 *    shall be included in all copies or substantial portions of this software.
 *  * The names of the authors may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 * 
 * Please cite
 * 
 * Matthias Rupp, Ewgenij Proschak, Gisbert Schneider:
 * A Kernel Approach to Molecular Similarity Based on Iterative Graph Similarity,
 * Journal of Chemical Information and Molecular Modeling, 47(6): 2280-2286, 2007, 
 * DOI http://dx.doi.org/10.1021/ci700274r.
 *
 * if you use this software.
 */

package info.mrupp.isoak1;

/** 
 * Precomputed factorial function.
 * 
 * Returns the factorial n*(n-1)*...*1 of the input argument n.
 * 
 * Implemented via tables for maximum speed. Runs in constant time.
 */

public class Factorial {
	private static final int[] intTable = { 
        1,         // 0!
		1,         // 1!
		2,         // 2!
		6,         // 3!
        24,        // 4!
        120,       // 5!
        720,       // 6!
        5040,      // 7!
        40320,     // 8!
        362880,    // 9!
        3628800,   // 10!
        39916800,  // 11!
        479001600  // 12!
	};
	
	private static final long[] longTable = {
        1L,                   // 0!
		1L,                   // 1!
		2L,                   // 2!
		6L,                   // 3!
        24L,                  // 4!
        120L,                 // 5!
        720L,                 // 6!
        5040L,                // 7!
        40320L,               // 8!
        362880L,              // 9!
        3628800L,             // 10!
        39916800L,            // 11!
        479001600L,           // 12!
        6227020800L,          // 13!
        87178291200L,         // 14!
        1307674368000L,       // 15!
        20922789888000L,      // 16!
        355687428096000L,     // 17!
        6402373705728000L,    // 18!
        121645100408832000L,  // 19!
        2432902008176640000L  // 20!
	}; 

    // Public interface.
    
    /** Provides precomputed results for the factorial function. */
    public Factorial() {}

    /** Returns the factorial for arguments 0,1,...,12. 
    *
    * Argument range is limited due to 13! being larger than the maximum integer.
    */
	public static int factorial(int n) { 
		try { return intTable[n]; }
		catch(IndexOutOfBoundsException e) { throw new ArithmeticException(e.getMessage()); }
	}

    /** Returns the factorial for arguments 0,1,...,20.
     * 
     * Argument range is limited due to 21! being larger than the maximum long integer.
     */
	public static long factorial(long n) { 
		try { return longTable[(int) (n)]; }
		catch(IndexOutOfBoundsException e) { throw new ArithmeticException(e.getMessage()); }
	}
}