Subversion Repositories Scribus

Rev

Rev 15347 | Go to most recent revision | Details | Compare with Previous | Last modification | View Log | RSS feed

Rev Author Line No. Line
15347 fschmid 1
/*
2
 * choose.h
12065 fschmid 3
 *
4
 * Copyright 2006 Nathan Hurst <njh@mail.csse.monash.edu.au>
5
 *
6
 * This library is free software; you can redistribute it and/or
7
 * modify it either under the terms of the GNU Lesser General Public
8
 * License version 2.1 as published by the Free Software Foundation
9
 * (the "LGPL") or, at your option, under the terms of the Mozilla
10
 * Public License Version 1.1 (the "MPL"). If you do not alter this
11
 * notice, a recipient may use your version of this file under either
12
 * the MPL or the LGPL.
13
 *
14
 * You should have received a copy of the LGPL along with this library
15
 * in the file COPYING-LGPL-2.1; if not, write to the Free Software
18122 mrdocs 16
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
12065 fschmid 17
 * You should have received a copy of the MPL along with this library
18
 * in the file COPYING-MPL-1.1
19
 *
20
 * The contents of this file are subject to the Mozilla Public License
21
 * Version 1.1 (the "License"); you may not use this file except in
22
 * compliance with the License. You may obtain a copy of the License at
23
 * http://www.mozilla.org/MPL/
24
 *
25
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY
26
 * OF ANY KIND, either express or implied. See the LGPL or the MPL for
27
 * the specific language governing rights and limitations.
28
 *
29
 */
30
 
31
#ifndef _CHOOSE_H
32
#define _CHOOSE_H
33
 
15347 fschmid 34
// XXX: Can we keep only the left terms easily? 
12065 fschmid 35
// this would more than halve the array
36
// row index becomes n2 = n/2, row2 = n2*(n2+1)/2, row = row2*2+(n&1)?n2:0
37
// we could also leave off the ones
38
 
39
template <typename T>
40
T choose(unsigned n, unsigned k) {
41
    static std::vector<T> pascals_triangle;
42
    static unsigned rows_done = 0;
43
    // indexing is (0,0,), (1,0), (1,1), (2, 0)...
44
    // to get (i, j) i*(i+1)/2 + j
15347 fschmid 45
    if(k < 0 || k > n) return 0;
12065 fschmid 46
    if(rows_done <= n) {// we haven't got there yet
47
        if(rows_done == 0) {
48
            pascals_triangle.push_back(1);
49
            rows_done = 1;
50
        }
51
        while(rows_done <= n) {
52
            unsigned p = pascals_triangle.size() - rows_done;
53
            pascals_triangle.push_back(1);
54
            for(unsigned i = 0; i < rows_done-1; i++) {
15347 fschmid 55
                pascals_triangle.push_back(pascals_triangle[p]
12065 fschmid 56
                                           + pascals_triangle[p+1]);
57
                p++;
58
            }
59
            pascals_triangle.push_back(1);
60
            rows_done ++;
61
        }
62
    }
63
    unsigned row = (n*(n+1))/2;
64
    return pascals_triangle[row+k];
65
}
66
 
67
#endif