71 lines
1.9 KiB
Rust
71 lines
1.9 KiB
Rust
use rand::{thread_rng, Rng};
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use crate::{normal_select::NormalSelect, Select};
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pub struct RandomizedSelect {
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comparisons: u64,
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swaps: u64,
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should_print: bool,
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normal: NormalSelect,
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}
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impl RandomizedSelect {
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fn rand_partition(&mut self, list: &mut Vec<u64>, lo: usize, hi: usize) -> usize {
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let pivot_index = thread_rng().gen_range(lo..hi);
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if self.should_print { println!("pivot_index: {pivot_index}"); }
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self.normal.partition(list, lo, hi, list[pivot_index])
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}
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fn _select(&mut self, list: &mut Vec<u64>, lo: usize, hi: usize, k: usize) -> (usize, u64) {
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if lo == hi {
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return (lo, list[lo]);
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}
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if self.should_print { println!("list: {:?}; lo: {lo}; hi: {hi}", list); }
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let r = self.rand_partition(list, lo, hi);
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if self.should_print { println!("r: {r}"); }
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self.comparisons += self.normal.num_comp();
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self.swaps += self.normal.num_swap();
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self.normal.reset_state();
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let i = r - lo + 1;
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if k == i {
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return (r, list[r]);
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} else if k < i {
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return self._select(list, lo, r - 1, k);
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} else {
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return self._select(list, r + 1, hi, k - i);
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}
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}
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}
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impl Select for RandomizedSelect {
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fn new(should_print: bool) -> Self {
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Self {
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comparisons: 0,
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swaps: 0,
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should_print,
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normal: NormalSelect::new(should_print),
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}
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}
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fn select_mut(&mut self, list: &mut Vec<u64>, order_statistic: usize) -> u64 {
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self._select(list, 0, list.len() - 1, order_statistic).1
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}
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fn num_comp(&self) -> u64 {
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self.comparisons
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}
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fn num_swap(&self) -> u64 {
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self.swaps
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}
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fn reset_state(&mut self) {
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self.comparisons = 0;
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self.swaps = 0;
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self.normal.reset_state();
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}
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}
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