Skip to content

HTTPS clone URL

Subversion checkout URL

You can clone with HTTPS or Subversion.

Download ZIP
Fetching contributors…

Cannot retrieve contributors at this time

69 lines (63 sloc) 1.758 kb
// Based on Isaac Gouy's fannkuchredux.csharp
use std;
import int;
import vec;
fn fannkuch(n: int) -> int {
fn perm1init(i: uint) -> int { ret i as int; }
let perm = vec::init_elt_mut(0, n as uint);
let perm1 = vec::init_fn_mut(perm1init, n as uint);
let count = vec::init_elt_mut(0, n as uint);
let f = 0;
let i = 0;
let k = 0;
let r = 0;
let flips = 0;
let nperm = 0;
let 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 go = true;
while go {
if r == n {
std::io::println(#fmt("%d", checksum));
ret 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;
}
ret flips;
}
fn main(args: [str]) {
let n = if vec::len(args) == 2u {
int::from_str(args[1])
} else {
8
};
std::io::println(#fmt("Pfannkuchen(%d) = %d", n, fannkuch(n)));
}
Jump to Line
Something went wrong with that request. Please try again.