82 lines
2.3 KiB
Rust
82 lines
2.3 KiB
Rust
// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
|
|
// file at the top-level directory of this distribution and at
|
|
// http://rust-lang.org/COPYRIGHT.
|
|
//
|
|
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
|
|
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
|
|
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
|
|
// option. This file may not be copied, modified, or distributed
|
|
// except according to those terms.
|
|
|
|
// Based on Isaac Gouy's fannkuchredux.csharp
|
|
extern mod std;
|
|
|
|
fn fannkuch(n: int) -> int {
|
|
fn perm1init(i: uint) -> int { return i as int; }
|
|
|
|
let mut perm = vec::from_elem(n as uint, 0);
|
|
let mut perm1 = vec::from_fn(n as uint, |i| perm1init(i));
|
|
let mut count = vec::from_elem(n as uint, 0);
|
|
let mut f = 0;
|
|
let mut i = 0;
|
|
let mut k = 0;
|
|
let mut r = 0;
|
|
let mut flips = 0;
|
|
let mut nperm = 0;
|
|
let mut checksum = 0;
|
|
r = n;
|
|
while r > 0 {
|
|
i = 0;
|
|
while r != 1 { count[r - 1] = r; r -= 1; }
|
|
while i < n { perm[i] = perm1[i]; i += 1; }
|
|
// Count flips and update max and checksum
|
|
|
|
f = 0;
|
|
k = perm[0];
|
|
while k != 0 {
|
|
i = 0;
|
|
while 2 * i < k {
|
|
let t = perm[i];
|
|
perm[i] = perm[k - i];
|
|
perm[k - i] = t;
|
|
i += 1;
|
|
}
|
|
k = perm[0];
|
|
f += 1;
|
|
}
|
|
if f > flips { flips = f; }
|
|
if nperm & 0x1 == 0 { checksum += f; } else { checksum -= f; }
|
|
// Use incremental change to generate another permutation
|
|
|
|
let mut go = true;
|
|
while go {
|
|
if r == n {
|
|
io::println(fmt!("%d", checksum));
|
|
return flips;
|
|
}
|
|
let p0 = perm1[0];
|
|
i = 0;
|
|
while i < r { let j = i + 1; perm1[i] = perm1[j]; i = j; }
|
|
perm1[r] = p0;
|
|
count[r] -= 1;
|
|
if count[r] > 0 { go = false; } else { r += 1; }
|
|
}
|
|
nperm += 1;
|
|
}
|
|
return flips;
|
|
}
|
|
|
|
fn main() {
|
|
let args = os::args();
|
|
let args = if os::getenv(~"RUST_BENCH").is_some() {
|
|
~[~"", ~"10"]
|
|
} else if args.len() <= 1u {
|
|
~[~"", ~"8"]
|
|
} else {
|
|
args
|
|
};
|
|
|
|
let n = int::from_str(args[1]).get();
|
|
io::println(fmt!("Pfannkuchen(%d) = %d", n, fannkuch(n)));
|
|
}
|