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// 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 perm = vec::to_mut(vec::from_elem(n as uint, 0));
let perm1 = vec::to_mut(vec::from_fn(n as uint, |i| perm1init(i)));
let count = vec::to_mut(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)));
}
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