From e9632af4480ade6e25d2891d275064c410f638a4 Mon Sep 17 00:00:00 2001
From: Rutherther <rutherther@ditigal.xyz>
Date: Sat, 1 Nov 2025 19:41:39 +0100
Subject: [PATCH] feat(tsp): add 2opt perturbation for subsequence reversal

---
 codes/tsp_hw01/src/perturbations.rs | 57 ++++++++++++++++++++++++++++-
 1 file changed, 55 insertions(+), 2 deletions(-)

diff --git a/codes/tsp_hw01/src/perturbations.rs b/codes/tsp_hw01/src/perturbations.rs
index f62385a0357f347d9a347b113545917ed3f0591e..a5c65d94623729d0655b27eb578fea81b4f9976b 100644
--- a/codes/tsp_hw01/src/perturbations.rs
+++ b/codes/tsp_hw01/src/perturbations.rs
@@ -1,8 +1,8 @@
 use std::marker::PhantomData;
 use nalgebra::{allocator::Allocator, DefaultAllocator, Dim};
 use rand::{Rng, RngCore};
-use eoa_lib::perturbation::PerturbationOperator;
-use crate::tsp::NodePermutation;
+use eoa_lib::{fitness::FitnessFunction, perturbation::PerturbationOperator};
+use crate::tsp::{NodePermutation, TSPInstance};
 
 pub struct SwapPerturbation<D> {
     _phantom: PhantomData<D>
@@ -120,3 +120,56 @@ where
         }
     }
 }
+
+pub struct Random2OptPerturbation<D>
+where
+    D: Dim,
+    DefaultAllocator: nalgebra::allocator::Allocator<D, D>
+{
+    instance: TSPInstance<D>,
+    retries: usize,
+    reversal: ReverseSubsequencePerturbation<D>,
+    _phantom: PhantomData<D>
+}
+
+impl<D> Random2OptPerturbation<D>
+where
+    D: Dim,
+    DefaultAllocator: nalgebra::allocator::Allocator<D, D>
+{
+    pub fn new(instance: &TSPInstance<D>, retries: usize) -> Self {
+        let mut reversal = ReverseSubsequencePerturbation::new();
+        reversal.min_subsequence_len = 5;
+        reversal.max_subsequence_len = 15;
+
+        Self {
+            retries,
+            instance: instance.clone(),
+            reversal,
+            _phantom: PhantomData
+        }
+    }
+}
+
+impl<D> PerturbationOperator for Random2OptPerturbation<D>
+where
+    D: Dim,
+    DefaultAllocator: nalgebra::allocator::Allocator<D>,
+    DefaultAllocator: nalgebra::allocator::Allocator<D, D>,
+{
+    type Chromosome = NodePermutation<D>;
+
+    fn perturb(&self, chromosome: &mut Self::Chromosome, rng: &mut dyn RngCore) {
+        let original_fitness = self.instance.fit(chromosome).unwrap();
+
+        for _ in 0..self.retries {
+            let mut cloned = chromosome.clone();
+            self.reversal.perturb(&mut cloned, rng);
+            let new_fitness = self.instance.fit(&cloned).unwrap();
+            if new_fitness < original_fitness {
+                std::mem::swap(chromosome, &mut cloned);
+                return;
+            }
+        }
+    }
+}