51 lines
1.3 KiB
Rust
51 lines
1.3 KiB
Rust
pub fn simple_hash(s: &str) -> usize {
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let mut h: u32 = 5381;
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for c in s.chars() {
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h = (h ^ c as u32).wrapping_add(h.rotate_right(6));
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}
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h as usize
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}
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/// Compute an open addressed, quadratically probed hash table containing
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/// `items`. The returned table is a list containing the elements of the
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/// iterable `items` and `None` in unused slots.
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pub fn generate_table<T, H: Fn(&T) -> usize>(items: &Vec<T>, hash_function: H) -> Vec<Option<&T>> {
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let size = (1.20 * items.len() as f64) as usize;
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// TODO do we really need the multiply by two here?
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let size = if size.is_power_of_two() {
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size * 2
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} else {
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size.next_power_of_two()
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};
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let mut table: Vec<Option<&T>> = Vec::new();
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table.resize(size, None);
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for i in items {
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let mut h = hash_function(i) % size;
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let mut s = 0;
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while table[h].is_some() {
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s += 1;
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h = (h + s) % size;
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}
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table[h] = Some(i);
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}
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table
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}
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#[test]
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fn test_generate_table() {
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let v = vec!["Hello".to_string(), "world".to_string()];
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let table = generate_table(&v, |s| simple_hash(&s));
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assert_eq!(
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table,
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vec![
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None,
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Some(&"Hello".to_string()),
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Some(&"world".to_string()),
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None
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]
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);
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}
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