feat: add FixedPoint crossover (#465)

<!-- If applicable - remember to add the PR to the EA Rust project (ONLY
IF THERE IS NO LINKED ISSUE) -->

## Description

Added `FixedPoint` crossover operator


## Linked issues

Resolves kkafar/master-monorepo#110


## Important implementation details

<!-- if any, optional section -->

examples/jssp/problem/individual.rs

@@ -55,7 +55,7 @@ impl PartialEq for JsspIndividual {
 impl Eq for JsspIndividual {}
 
 impl PartialOrd for JsspIndividual {
-    #[allow(clippy::incorrect_partial_ord_impl_on_ord_type)]
+    #[allow(clippy::non_canonical_partial_ord_impl)]
     fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
         self.fitness.partial_cmp(&other.fitness)
     }

src/ga/individual.rs

@@ -146,7 +146,7 @@ impl<T: Chromosome> PartialEq<Self> for Individual<T> {
 impl<T: Chromosome> Eq for Individual<T> {}
 
 impl<T: Chromosome> PartialOrd<Self> for Individual<T> {
-    #[allow(clippy::incorrect_partial_ord_impl_on_ord_type)]
+    #[allow(clippy::non_canonical_partial_ord_impl)]
     fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
         self.fitness.partial_cmp(&other.fitness)
     }

src/ga/operators/crossover.rs

@@ -2,7 +2,7 @@ use itertools::{enumerate, Itertools};
 use len_trait::Len;
 use std::collections::{HashMap, HashSet};
 use std::hash::Hash;
-use std::ops::Index;
+use std::ops::{Index, IndexMut};
 
 use crate::ga::individual::{Chromosome, IndividualTrait};
 use push_trait::{Nothing, Push};
@@ -913,11 +913,58 @@ where
     }
 }
 
+/// # Fixed point crossover operator
+///
+/// Works just like `SinglePoint`, however the cut point is fixed and chosen apriori instead of
+/// being random.
+struct FixedPoint {
+    pub cut_point: usize,
+}
+
+impl FixedPoint {
+    /// Returns new instance of the `FixedPoint` operator.
+    ///
+    /// # Arguments
+    ///
+    /// * `cut_point` - index of first gene that will be taken from second parent to first child
+    pub fn new(cut_point: usize) -> Self {
+        Self { cut_point }
+    }
+}
+
+impl<GeneT, IndividualT> CrossoverOperator<IndividualT> for FixedPoint
+where
+    IndividualT: IndividualTrait,
+    IndividualT::ChromosomeT: IndexMut<usize, Output = GeneT> + Push<GeneT, PushedOut = Nothing>,
+    GeneT: Copy,
+{
+    /// Returns a tuple of children
+    ///
+    /// It works by cutting parent chromosomes in single, fixed point and the acting like a single
+    /// point crossover.
+    ///
+    /// # Arguments
+    ///
+    /// * `parent_1` - First parent to take part in recombination
+    /// * `parent_2` - Second parent to take part in recombination
+    fn apply(&mut self, parent_1: &IndividualT, parent_2: &IndividualT) -> (IndividualT, IndividualT) {
+        let mut child_1 = parent_1.clone();
+        let mut child_2 = parent_2.clone();
+
+        for i in self.cut_point..parent_1.chromosome().len() {
+            child_1.chromosome_mut()[i] = parent_2.chromosome()[i];
+            child_2.chromosome_mut()[i] = parent_1.chromosome()[i];
+        }
+
+        (child_1, child_2)
+    }
+}
+
 #[cfg(test)]
 mod test {
     use crate::ga::individual::IndividualTrait;
     use crate::ga::operators::crossover::Ppx;
-    use crate::ga::operators::crossover::{CrossoverOperator, Pmx, Shuffle};
+    use crate::ga::operators::crossover::{CrossoverOperator, FixedPoint, Pmx, Shuffle};
     use crate::ga::Individual;
     use std::iter::zip;
 
@@ -976,4 +1023,23 @@ mod test {
             assert_eq!(g1 + g2, 1);
         }
     }
+
+    #[test]
+    fn fixed_point_works_as_expected() {
+        let mut op = FixedPoint::new(4);
+
+        let parent_1_chromosome = vec![8, 4, 7, 3, 6, 2, 5, 1, 9, 0];
+        let parent_2_chromosome = vec![0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
+
+        let p1 = Individual::from(parent_1_chromosome.clone());
+        let p2 = Individual::from(parent_2_chromosome.clone());
+
+        let (child_1, child_2) = op.apply(&p1, &p2);
+
+        let child_1_expected_chromosome = vec![8, 4, 7, 3, 4, 5, 6, 7, 8, 9];
+        let child_2_expected_chromosome = vec![0, 1, 2, 3, 6, 2, 5, 1, 9, 0];
+
+        assert_eq!(child_1.chromosome(), &child_1_expected_chromosome);
+        assert_eq!(child_2.chromosome(), &child_2_expected_chromosome);
+    }
 }