71 lines
1.9 KiB
Rust
71 lines
1.9 KiB
Rust
// Based on Isaac Gouy's fannkuchredux.csharp
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extern mod std;
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fn fannkuch(n: int) -> int {
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fn perm1init(i: uint) -> int { return i as int; }
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let perm = vec::to_mut(vec::from_elem(n as uint, 0));
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let perm1 = vec::to_mut(vec::from_fn(n as uint, perm1init));
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let count = vec::to_mut(vec::from_elem(n as uint, 0));
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let mut f = 0;
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let mut i = 0;
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let mut k = 0;
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let mut r = 0;
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let mut flips = 0;
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let mut nperm = 0;
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let mut checksum = 0;
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r = n;
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while r > 0 {
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i = 0;
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while r != 1 { count[r - 1] = r; r -= 1; }
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while i < n { perm[i] = perm1[i]; i += 1; }
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// Count flips and update max and checksum
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f = 0;
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k = perm[0];
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while k != 0 {
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i = 0;
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while 2 * i < k {
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let t = perm[i];
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perm[i] = perm[k - i];
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perm[k - i] = t;
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i += 1;
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}
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k = perm[0];
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f += 1;
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}
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if f > flips { flips = f; }
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if nperm & 0x1 == 0 { checksum += f; } else { checksum -= f; }
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// Use incremental change to generate another permutation
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let mut go = true;
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while go {
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if r == n {
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io::println(fmt!("%d", checksum));
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return flips;
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}
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let p0 = perm1[0];
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i = 0;
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while i < r { let j = i + 1; perm1[i] = perm1[j]; i = j; }
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perm1[r] = p0;
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count[r] -= 1;
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if count[r] > 0 { go = false; } else { r += 1; }
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}
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nperm += 1;
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}
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return flips;
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}
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fn main(args: ~[~str]) {
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let args = if os::getenv(~"RUST_BENCH").is_some() {
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~[~"", ~"10"]
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} else if args.len() <= 1u {
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~[~"", ~"8"]
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} else {
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args
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};
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let n = int::from_str(args[1]).get();
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io::println(fmt!("Pfannkuchen(%d) = %d", n, fannkuch(n)));
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}
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