Fix Engine: Refactor conflict handling in lower and upper bound methods to improve clarity and consistency

Author: riccardodebenedictis

src/lib.rs

@@ -119,7 +119,7 @@ impl Engine {
             if let Some(reason) = reason {
                 self.conflict.push(reason);
             }
-            for reason in self.ubs[var].iter().next_back().unwrap().1.iter() {
+            for reason in self.ubs[var].iter().next().unwrap().1.iter() {
                 self.conflict.push(*reason);
             }
             return false; // Inconsistent constraint
@@ -137,7 +137,10 @@ impl Engine {
             }
         }
 
-        self.lbs[var].entry(lb).or_default().insert(reason.unwrap());
+        let entry = self.lbs[var].entry(lb).or_default();
+        if let Some(reason) = reason {
+            entry.insert(reason);
+        }
         if self.value(var) < &lb && !self.is_basic(var) {
             self.update(var, lb);
         }
@@ -151,7 +154,7 @@ impl Engine {
             if let Some(reason) = reason {
                 self.conflict.push(reason);
             }
-            for reason in self.lbs[var].iter().next().unwrap().1.iter() {
+            for reason in self.lbs[var].iter().next_back().unwrap().1.iter() {
                 self.conflict.push(*reason);
             }
             return false; // Inconsistent constraint
@@ -169,7 +172,10 @@ impl Engine {
             }
         }
 
-        self.ubs[var].entry(ub).or_default().insert(reason.unwrap());
+        let entry = self.ubs[var].entry(ub).or_default();
+        if let Some(reason) = reason {
+            entry.insert(reason);
+        }
         if self.value(var) > &ub && !self.is_basic(var) {
             self.update(var, ub);
         }