Add reverse to OrderMapCore, IndexMap, IndexSet

Author: linclelinkpart5

src/map.rs

@@ -1253,6 +1253,13 @@ where
         self.into_iter()
     }
 
+    /// Reverses the order of the map’s key-value pairs in place.
+    ///
+    /// Computes in **O(n)** time and **O(1)** space.
+    pub fn reverse(&mut self) {
+        self.core.reverse()
+    }
+
     /// Clears the `IndexMap`, returning all key-value pairs as a drain iterator.
     /// Keeps the allocated memory for reuse.
     pub fn drain(&mut self, range: RangeFull) -> Drain<K, V> {
@@ -1752,6 +1759,12 @@ impl<K, V> OrderMapCore<K, V> {
         self.restore_hash_index(side_index);
     }
 
+    fn reverse(&mut self) {
+        let side_index = self.save_hash_index();
+        self.entries.reverse();
+        self.restore_hash_index(side_index);
+    }
+
     fn save_hash_index(&mut self) -> Vec<usize> {
         // Temporarily use the hash field in a bucket to store the old index.
         // Save the old hash values in `side_index`.  Then we can sort

src/set.rs

@@ -527,6 +527,13 @@ where
         }
     }
 
+    /// Reverses the order of the set’s values in place.
+    ///
+    /// Computes in **O(n)** time and **O(1)** space.
+    pub fn reverse(&mut self) {
+        self.map.reverse()
+    }
+
     /// Clears the `IndexSet`, returning all values as a drain iterator.
     /// Keeps the allocated memory for reuse.
     pub fn drain(&mut self, range: RangeFull) -> Drain<T> {