From 8eaf8145d149098a0ef70811ce8ea9c98447eb11 Mon Sep 17 00:00:00 2001
From: Rutherther <rutherther@ditigal.xyz>
Date: Sat, 1 Nov 2025 10:23:59 +0100
Subject: [PATCH] fix(tsp): properly implement binary string -> node
 permutation fitness

---
 codes/tsp_hw01/src/tsp.rs | 123 ++++++++++++++++++++++++--------------
 1 file changed, 77 insertions(+), 46 deletions(-)

diff --git a/codes/tsp_hw01/src/tsp.rs b/codes/tsp_hw01/src/tsp.rs
index d95714b4ffb9e22d4a439712ff29df113b3c6325..a4c6d39a31f54ad072ed979d58384e18bbd9f2c4 100644
--- a/codes/tsp_hw01/src/tsp.rs
+++ b/codes/tsp_hw01/src/tsp.rs
@@ -452,89 +452,120 @@ where
     }
 }
 
-pub struct BinaryStringToNodePermutation<DIn: Dim, DOut: Dim> {
+pub struct TSPBinaryStringWrapper<'a, DIn: Dim, DOut: Dim>
+where
+    DOut: Dim,
+    DefaultAllocator: Allocator<DOut, DOut>
+{
+    instance: &'a TSPInstance<DOut>,
     dim_in: DIn,
     dim_out: DOut,
 }
 
-impl<DIn: Dim, DOut: Dim> BinaryStringToNodePermutation<DIn, DOut> {
-    pub fn new(dim_in: DIn, dim_out: DOut) -> Self {
-        Self {
+impl<'a, DIn: Dim, DOut: Dim> TSPBinaryStringWrapper<'a, DIn, DOut>
+where
+    DOut: Dim,
+    DefaultAllocator: Allocator<DOut, DOut>,
+    DefaultAllocator: Allocator<DIn>,
+    DefaultAllocator: Allocator<DOut>,
+{
+    pub fn new(
+        instance: &'a TSPInstance<DOut>,
+        dim_in: DIn,
+        dim_out: DOut
+    ) -> Result<Self, DimensionMismatch> {
+        let res = Self {
+            instance,
             dim_in,
             dim_out
+        };
+
+        if dim_out.value() * (dim_out.value() - 1) / 2 != dim_in.value() {
+            Err(DimensionMismatch::Mismatch)
+        } else {
+            Ok(res)
         }
     }
-}
 
-#[derive(Error, Debug)]
-pub enum DimensionMismatch {
-    #[error("The input dimension should be equal to half matrix NxN where the output is N")]
-    Mismatch
-}
+    pub fn to_permutation(&self, inp: &BinaryString<DIn>) -> Result<NodePermutation<DOut>, DimensionMismatch> {
+        let nodes = self.dim_out.value();
 
-impl<DIn: Dim, DOut: Dim> FitnessFunction for BinaryStringToNodePermutation<DIn, DOut>
-where
-    DefaultAllocator: Allocator<DIn>,
-    DefaultAllocator: Allocator<DOut>,
-    DefaultAllocator: Allocator<DOut, DOut>,
-{
-    type In = BinaryString<DIn>;
-    type Out = NodePermutation<DOut>;
-    type Err = DimensionMismatch;
+        if inp.vec().shape_generic().0.value() != self.dim_in.value() {
+            return Err(DimensionMismatch::Mismatch);
+        }
 
-    fn fit(self: &Self, inp: &Self::In) -> Result<Self::Out, Self::Err> {
-        let nodes = self.dim_out.value();
-        let mut orderings =
-            OMatrix::<Ordering, DOut, DOut>::from_element_generic(self.dim_out, self.dim_out, Ordering::Equal);
+        // Count how many nodes each node comes after (precedence count)
+        let mut precedence_count = OVector::<usize, DOut>::zeros_generic(self.dim_out, U1);
 
         let mut in_index = 0usize;
         for i in 0..self.dim_out.value() {
-            for j in i+1..self.dim_out.value() {
-                orderings[(i, j)] = if inp.vec[in_index] == 1 {
-                    Ordering::Greater
-                } else {
-                    Ordering::Less
-                };
+            for j in i+1..nodes {
+                if in_index >= inp.vec.len() {
+                    return Err(DimensionMismatch::Mismatch);
+                }
 
-                orderings[(j, i)] = if inp.vec[in_index] == 1 {
-                    Ordering::Less
+                if inp.vec[in_index] == 1 {
+                    // i comes before j, so j has one more predecessor
+                    precedence_count[j] += 1;
                 } else {
-                    Ordering::Greater
-                };
+                    // j comes before i, so i has one more predecessor
+                    precedence_count[i] += 1;
+                }
 
                 in_index += 1;
             }
         }
 
-        let mut result =
-            OVector::from_iterator_generic(self.dim_out, U1, 0..nodes);
+        if in_index != inp.vec.len() {
+            return Err(DimensionMismatch::Mismatch);
+        }
 
-        for i in 0..nodes {
-            for j in i+1..nodes {
-                let node1 = result[i];
-                let node2 = result[j];
+        let mut result = OVector::from_iterator_generic(
+            self.dim_out,
+            U1,
+            0..nodes
+        );
 
-                if orderings[(node1, node2)] == Ordering::Greater {
-                    result.swap_rows(i, j);
-                }
-            }
-        }
+        result
+            .as_mut_slice()
+            .sort_by_key(|&node| precedence_count[node]);
 
         Ok(NodePermutation { permutation: result })
     }
 }
 
+#[derive(Error, Debug)]
+pub enum DimensionMismatch {
+    #[error("The input dimension should be equal to half matrix NxN where the output is N")]
+    Mismatch
+}
+
+impl<'a, DIn: Dim, DOut: Dim> FitnessFunction for TSPBinaryStringWrapper<'a, DIn, DOut>
+where
+    DefaultAllocator: Allocator<DIn>,
+    DefaultAllocator: Allocator<DOut>,
+    DefaultAllocator: Allocator<DOut, DOut>,
+{
+    type In = BinaryString<DIn>;
+    type Out = f64;
+    type Err = DimensionMismatch;
+
+    fn fit(self: &Self, inp: &Self::In) -> Result<Self::Out, Self::Err> {
+        Ok(self.instance.fit(&self.to_permutation(inp)?).unwrap())
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use std::convert::Infallible;
 
     use eoa_lib::{binary_string::BinaryString, crossover::Crossover, fitness::FitnessFunction, initializer::Initializer, pairing::{AdjacentPairing, Pairing}, replacement::Population};
     use nalgebra::{Const, SVector, U15, U6};
-    use rand::{rngs::StdRng, RngCore, SeedableRng};
+    use rand::{rngs::StdRng, seq::SliceRandom, RngCore, SeedableRng};
 
     use crate::tsp::TSPInstance;
 
-    use super::{BinaryStringToNodePermutation, EdgeRecombinationCrossover, NodePermutation, ReverseSubsequencePerturbation, TSPRandomInitializer};
+    use super::{TSPBinaryStringWrapper, EdgeRecombinationCrossover, NodePermutation, ReverseSubsequencePerturbation, TSPRandomInitializer};
     use eoa_lib::perturbation::PerturbationOperator;
 
     struct MockRng;