Add parameter parser and TreeDecomposition

Cargo.toml

@@ -7,6 +7,8 @@ description = "Utilities to read PACE26 instances and write answers"
 license = "GPL-3.0-or-later"
 
 [dependencies]
+serde = "1.0.228"
+serde_json = "1.0.145"
 thiserror = "2.0.17"
 
 [dev-dependencies]

src/pace/mod.rs

@@ -1 +1,2 @@
+pub mod parameters;
 pub mod reader;

src/pace/parameters/mod.rs

@@ -0,0 +1 @@
+pub mod tree_decomposition;

src/pace/parameters/tree_decomposition.rs

@@ -0,0 +1,71 @@
+use serde::de::{self, Deserialize, Deserializer, SeqAccess, Visitor};
+use std::fmt;
+
+type Node = u32;
+type NumNodes = Node;
+
+/// Container to store the `treedecomp` parameter.
+/// Recall that all indices are 1-index, i.e. the edge `(u,v)` refers to `bags[u-1]` and `bags[v-1]`.
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub struct TreeDecomposition {
+    pub treewidth: NumNodes,
+    pub bags: Vec<Vec<Node>>,
+    pub edges: Vec<(Node, Node)>,
+}
+
+impl<'de> Deserialize<'de> for TreeDecomposition {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        struct TreeDecompositionVisitor;
+
+        impl<'de> Visitor<'de> for TreeDecompositionVisitor {
+            type Value = TreeDecomposition;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                formatter.write_str("a sequence of three elements: treewidth, bags, edges")
+            }
+
+            fn visit_seq<A>(self, mut seq: A) -> Result<TreeDecomposition, A::Error>
+            where
+                A: SeqAccess<'de>,
+            {
+                let treewidth: NumNodes = seq
+                    .next_element()?
+                    .ok_or_else(|| de::Error::invalid_length(0, &self))?;
+
+                let bags: Vec<Vec<Node>> = seq
+                    .next_element()?
+                    .ok_or_else(|| de::Error::invalid_length(1, &self))?;
+
+                let edges: Vec<(Node, Node)> = seq
+                    .next_element()?
+                    .ok_or_else(|| de::Error::invalid_length(2, &self))?;
+
+                Ok(TreeDecomposition {
+                    treewidth,
+                    bags,
+                    edges,
+                })
+            }
+        }
+
+        deserializer.deserialize_seq(TreeDecompositionVisitor)
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use crate::pace::parameters::tree_decomposition::TreeDecomposition;
+
+    #[test]
+    fn json_to_tree_decomp() {
+        const JSON: &str = "[2,[[8,16],[8,11,16],[1,11,15],[2,11,16],[7,8,11],[8,10,16],[3,10,13],[4,10,16],[8,9],[5,9,14],[6,9,12]],[[1,2],[1,6],[1,9],[2,3],[2,4],[2,5],[6,7],[6,8],[9,10],[9,11]]]";
+        let td: TreeDecomposition = serde_json::from_str(JSON).unwrap();
+
+        assert_eq!(td.treewidth, 2);
+        assert_eq!(td.bags.len(), 11);
+        assert_eq!(td.edges.len(), 10);
+    }
+}