// Based on Isaac Gouy's fannkuchredux.csharp
use std;
import std::int;
import std::vec;

fn fannkuch(n: int) -> int {
    fn perm1init(i: uint) -> int { ret i as int; }
    let perm1init_ = perm1init; // Rustboot workaround

    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 { log 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 = 7;
    log #fmt("Pfannkuchen(%d) = %d", n, fannkuch(n));
}