Apply suggestions from code review

Co-authored-by: Austin Huang <[email protected]>

Author: Jaybsoni

pennylane/estimator/compact_hamiltonian.py

@@ -422,12 +422,9 @@ def _validate_pauli_dist(pauli_dist: dict) -> bool:
 
 def _pauli_dist_from_commuting_groups(commuting_groups: tuple[dict]):
     """Construct the total Pauli word distribution from the commuting groups."""
-    total_pauli_dist = defaultdict(int)
-
+    total_pauli_dist = Counter()
     for group in commuting_groups:
-        for pauli_word, frequency in group.items():
-            total_pauli_dist[pauli_word] += frequency
-
+        total_pauli_dist.update(group)
     return total_pauli_dist
 
 

pennylane/estimator/templates/trotter.py

@@ -2097,8 +2097,7 @@ def cost_pauli_group(pauli_dist: dict):
                 a commuting group of Pauli words.
 
         """
-        gate_count_lst = []
-        for pauli_word, count in pauli_dist.items():
-            gate_count_lst.append(GateCount(PauliRot.resource_rep(pauli_word), count))
-
-        return gate_count_lst
+return [
+    GateCount(PauliRot.resource_rep(pauli_word), count)
+    for pauli_word, count in pauli_dist.items()
+]