108 lines
3.1 KiB
Rust
108 lines
3.1 KiB
Rust
// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
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// file at the top-level directory of this distribution and at
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// http://rust-lang.org/COPYRIGHT.
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//
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// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
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// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
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// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
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// option. This file may not be copied, modified, or distributed
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// except according to those terms.
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// ignore-test reading from os::args()[1] - bogus!
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use std::from_str::FromStr;
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use std::os;
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use std::vec::MutableVector;
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use std::vec;
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fn max(a: i32, b: i32) -> i32 {
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if a > b {
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a
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} else {
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b
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}
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}
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#[inline(never)]
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fn fannkuch_redux(n: i32) -> i32 {
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let mut perm = vec::from_elem(n as uint, 0i32);
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let mut perm1 = vec::from_fn(n as uint, |i| i as i32);
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let mut count = vec::from_elem(n as uint, 0i32);
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let mut max_flips_count = 0i32;
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let mut perm_count = 0i32;
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let mut checksum = 0i32;
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let mut r = n;
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loop {
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unsafe {
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while r != 1 {
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count.unsafe_set((r-1) as uint, r);
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r -= 1;
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}
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for (perm_i, perm1_i) in perm.mut_iter().zip(perm1.iter()) {
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*perm_i = *perm1_i;
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}
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let mut flips_count: i32 = 0;
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let mut k: i32;
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loop {
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k = *perm.unsafe_ref(0);
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if k == 0 {
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break;
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}
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let k2 = (k+1) >> 1;
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for i in range(0i32, k2) {
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let (perm_i, perm_k_i) = {
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(*perm.unsafe_ref(i as uint),
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*perm.unsafe_ref((k-i) as uint))
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};
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perm.unsafe_set(i as uint, perm_k_i);
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perm.unsafe_set((k-i) as uint, perm_i);
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}
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flips_count += 1;
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}
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max_flips_count = max(max_flips_count, flips_count);
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checksum += if perm_count % 2 == 0 {
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flips_count
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} else {
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-flips_count
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};
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// Use incremental change to generate another permutation.
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loop {
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if r == n {
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println!("{}", checksum);
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return max_flips_count;
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}
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let perm0 = perm1[0];
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let mut i: i32 = 0;
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while i < r {
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let j = i + 1;
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let perm1_j = { *perm1.unsafe_ref(j as uint) };
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perm1.unsafe_set(i as uint, perm1_j);
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i = j;
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}
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perm1.unsafe_set(r as uint, perm0);
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let count_r = { *count.unsafe_ref(r as uint) };
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count.unsafe_set(r as uint, count_r - 1);
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if *count.unsafe_ref(r as uint) > 0 {
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break;
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}
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r += 1;
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}
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perm_count += 1;
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}
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}
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}
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fn main() {
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let n: i32 = FromStr::from_str(os::args()[1]).unwrap();
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println!("Pfannkuchen({}) = {}", n as int, fannkuch_redux(n) as int);
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}
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