27 lines
989 B
Rust
27 lines
989 B
Rust
#[cfg(test)]
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mod tests;
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/// Uses a sorted slice `data: &[E]` as a kind of "multi-map". The
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/// `key_fn` extracts a key of type `K` from the data, and this
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/// function finds the range of elements that match the key. `data`
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/// must have been sorted as if by a call to `sort_by_key` for this to
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/// work.
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pub fn binary_search_slice<'d, E, K>(data: &'d [E], key_fn: impl Fn(&E) -> K, key: &K) -> &'d [E]
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where
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K: Ord,
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{
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let size = data.len();
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let start = data.partition_point(|x| key_fn(x) < *key);
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// At this point `start` either points at the first entry with equal or
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// greater key or is equal to `size` in case all elements have smaller keys
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if start == size || key_fn(&data[start]) != *key {
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return &[];
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};
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// Find the first entry with key > `key`. Skip `start` entries since
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// key_fn(&data[start]) == *key
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let offset = start + 1;
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let end = data[offset..].partition_point(|x| key_fn(x) <= *key) + offset;
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&data[start..end]
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}
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