72 lines
1.6 KiB
Rust
72 lines
1.6 KiB
Rust
use rand::prelude::*;
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use std::cmp::Ordering;
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pub fn post_inc(value: &mut usize) -> usize {
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let prev = *value;
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*value += 1;
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prev
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}
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pub fn find_insertion_index<'a, F, T, E>(slice: &'a [T], mut f: F) -> Result<usize, E>
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where
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F: FnMut(&'a T) -> Result<Ordering, E>,
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{
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use Ordering::*;
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let s = slice;
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let mut size = s.len();
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if size == 0 {
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return Ok(0);
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}
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let mut base = 0usize;
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while size > 1 {
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let half = size / 2;
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let mid = base + half;
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// mid is always in [0, size), that means mid is >= 0 and < size.
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// mid >= 0: by definition
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// mid < size: mid = size / 2 + size / 4 + size / 8 ...
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let cmp = f(unsafe { s.get_unchecked(mid) })?;
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base = if cmp == Greater { base } else { mid };
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size -= half;
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}
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// base is always in [0, size) because base <= mid.
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let cmp = f(unsafe { s.get_unchecked(base) })?;
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if cmp == Equal {
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Ok(base)
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} else {
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Ok(base + (cmp == Less) as usize)
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}
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}
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pub struct RandomCharIter<T: Rng>(T);
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impl<T: Rng> RandomCharIter<T> {
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pub fn new(rng: T) -> Self {
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Self(rng)
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}
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}
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impl<T: Rng> Iterator for RandomCharIter<T> {
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type Item = char;
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fn next(&mut self) -> Option<Self::Item> {
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if self.0.gen_bool(1.0 / 5.0) {
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Some('\n')
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} else {
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Some(self.0.gen_range(b'a'..b'z' + 1).into())
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}
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}
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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#[test]
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fn test_find_insertion_index() {
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assert_eq!(
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find_insertion_index(&[0, 4, 8], |probe| Ok::<Ordering, ()>(probe.cmp(&2))),
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Ok(1)
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);
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}
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}
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