1/*
2Redistribution and use in source and binary forms, with or without
3modification, are permitted provided that the following conditions are met:
4
5    * Redistributions of source code must retain the above copyright
6    notice, this list of conditions and the following disclaimer.
7
8    * Redistributions in binary form must reproduce the above copyright
9    notice, this list of conditions and the following disclaimer in the
10    documentation and/or other materials provided with the distribution.
11
12    * Neither the name of "The Computer Language Benchmarks Game" nor the
13    name of "The Computer Language Shootout Benchmarks" nor the names of
14    its contributors may be used to endorse or promote products derived
15    from this software without specific prior written permission.
16
17THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
18AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
19IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
20ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
21LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
22CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
23SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
24INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
25CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
26ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
27POSSIBILITY OF SUCH DAMAGE.
28*/
29
30/*
31 * The Computer Language Benchmarks Game
32 * http://shootout.alioth.debian.org/
33 *
34 * contributed by The Go Authors.
35 * Based on fannkuch.c by Heiner Marxen
36 */
37
38package main
39
40import (
41	"flag"
42	"fmt"
43)
44
45var n = flag.Int("n", 7, "count")
46
47func fannkuch(n int) int {
48	if n < 1 {
49		return 0
50	}
51
52	n1 := n - 1
53	perm := make([]int, n)
54	perm1 := make([]int, n)
55	count := make([]int, n)
56
57	for i := 0; i < n; i++ {
58		perm1[i] = i // initial (trivial) permutation
59	}
60
61	r := n
62	didpr := 0
63	flipsMax := 0
64	for {
65		if didpr < 30 {
66			for i := 0; i < n; i++ {
67				fmt.Printf("%d", 1+perm1[i])
68			}
69			fmt.Printf("\n")
70			didpr++
71		}
72		for ; r != 1; r-- {
73			count[r-1] = r
74		}
75
76		if perm1[0] != 0 && perm1[n1] != n1 {
77			flips := 0
78			for i := 1; i < n; i++ { // perm = perm1
79				perm[i] = perm1[i]
80			}
81			k := perm1[0] // cache perm[0] in k
82			for {         // k!=0 ==> k>0
83				for i, j := 1, k-1; i < j; i, j = i+1, j-1 {
84					perm[i], perm[j] = perm[j], perm[i]
85				}
86				flips++
87				// Now exchange k (caching perm[0]) and perm[k]... with care!
88				j := perm[k]
89				perm[k] = k
90				k = j
91				if k == 0 {
92					break
93				}
94			}
95			if flipsMax < flips {
96				flipsMax = flips
97			}
98		}
99
100		for ; r < n; r++ {
101			// rotate down perm[0..r] by one
102			perm0 := perm1[0]
103			for i := 0; i < r; i++ {
104				perm1[i] = perm1[i+1]
105			}
106			perm1[r] = perm0
107			count[r]--
108			if count[r] > 0 {
109				break
110			}
111		}
112		if r == n {
113			return flipsMax
114		}
115	}
116	return 0
117}
118
119func main() {
120	flag.Parse()
121	fmt.Printf("Pfannkuchen(%d) = %d\n", *n, fannkuch(*n))
122}
123