Refactor some of the patience code into a utils module

src/algorithms/utils.rs

@@ -1,7 +1,69 @@
-use std::ops::Range;
+use std::collections::hash_map::Entry;
+use std::collections::HashMap;
+use std::hash::Hash;
+use std::ops::{Index, Range};
 
 /// Utility function to check if a range is empty that works on older rust versions
 #[inline(always)]
-pub(crate) fn is_empty_range<T: PartialOrd>(range: &Range<T>) -> bool {
+pub fn is_empty_range<T: PartialOrd>(range: &Range<T>) -> bool {
     !(range.start < range.end)
 }
+pub struct Indexable<'a, Idx: ?Sized> {
+    lookup: &'a Idx,
+    index: usize,
+}
+
+impl<'a, Idx: ?Sized> Indexable<'a, Idx> {
+    /// Returns the index.
+    pub fn index(&self) -> usize {
+        self.index
+    }
+}
+
+impl<'a, Idx: Index<usize> + 'a> std::fmt::Debug for Indexable<'a, Idx>
+where
+    Idx::Output: std::fmt::Debug,
+{
+    fn fmt(&self, fmt: &mut std::fmt::Formatter) -> std::fmt::Result {
+        write!(fmt, "{:?}", &self.lookup[self.index])
+    }
+}
+
+impl<'a, 'b, A, B> PartialEq<Indexable<'a, A>> for Indexable<'b, B>
+where
+    A: Index<usize> + 'b + ?Sized,
+    B: Index<usize> + 'b + ?Sized,
+    B::Output: PartialEq<A::Output>,
+{
+    fn eq(&self, b: &Indexable<'a, A>) -> bool {
+        self.lookup[self.index] == b.lookup[b.index]
+    }
+}
+
+pub fn unique<Idx>(seq: &Idx, range: Range<usize>) -> Vec<Indexable<Idx>>
+where
+    Idx: Index<usize> + ?Sized,
+    Idx::Output: Hash + Eq,
+{
+    let mut by_item = HashMap::new();
+    for index in range {
+        match by_item.entry(&seq[index]) {
+            Entry::Vacant(entry) => {
+                entry.insert(Some(index));
+            }
+            Entry::Occupied(mut entry) => {
+                let entry = entry.get_mut();
+                if entry.is_some() {
+                    *entry = None
+                }
+            }
+        }
+    }
+    let mut rv = by_item
+        .into_iter()
+        .filter_map(|(_, x)| x)
+        .map(|index| Indexable { lookup: seq, index })
+        .collect::<Vec<_>>();
+    rv.sort_by(|a, b| a.index.cmp(&b.index));
+    rv
+}