62 lines
1.6 KiB
Rust
62 lines
1.6 KiB
Rust
// Based on Isaac Gouy's fannkuchredux.csharp
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use std;
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import std::int;
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import std::vec;
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fn fannkuch(n: int) -> int {
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fn perm1init(i: uint) -> int { ret i as int; }
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let perm1init_ = perm1init; // Rustboot workaround
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let perm = vec::init_elt_mut(0, n as uint);
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let perm1 = vec::init_fn_mut(perm1init_, n as uint);
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let count = vec::init_elt_mut(0, n as uint);
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let f = 0;
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let i = 0;
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let k = 0;
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let r = 0;
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let flips = 0;
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let nperm = 0;
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let 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 go = true;
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while go {
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if r == n { log checksum; ret flips; }
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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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ret flips;
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}
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fn main(args: [str]) {
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let n = 7;
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log #fmt("Pfannkuchen(%d) = %d", n, fannkuch(n));
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} |