imported patch tarjan-deque.patch

prism/src/explicit/SCCComputerTarjan.java

@@ -29,8 +29,8 @@ package explicit;
 
 import java.util.ArrayList;
 import java.util.BitSet;
+import java.util.Deque;
 import java.util.LinkedList;
-import java.util.List;
 import java.util.function.IntPredicate;
 
 import prism.PrismComponent;
@@ -49,7 +49,7 @@ public class SCCComputerTarjan extends SCCComputer
 	/* Next index to give to a node */
 	private int index = 0;
 	/* Stack of nodes */
-	private List<Integer> stack = new LinkedList<Integer>();
+	private Deque<Integer> stack = new LinkedList<Integer>();
 	/* List of nodes in the graph. Invariant: {@code nodeList.get(i).id == i} */
 	private ArrayList<Node> nodeList;
 	/* Nodes currently on the stack. */
@@ -108,7 +108,7 @@ public class SCCComputerTarjan extends SCCComputer
 		v.index = index;
 		v.lowlink = index;
 		index++;
-		stack.add(0, i);
+		stack.push(i);
 		onStack.set(i);
 
 		boolean hadSelfloop = false;
@@ -135,10 +135,10 @@ public class SCCComputerTarjan extends SCCComputer
 		}
 		if (v.lowlink == v.index) {
 			// this is a singleton SCC if the top of the stack equals i
-			boolean singletonSCC = (stack.get(0) == i);
+			boolean singletonSCC = (stack.peek() == i);
 			if (singletonSCC && filterTrivialSCCs) {
 				if (!hadSelfloop) { // singleton SCC & no selfloop -> trivial
-					stack.remove(0);
+					stack.pop();
 					onStack.set(i, false);
 					return;
 				}
@@ -147,7 +147,7 @@ public class SCCComputerTarjan extends SCCComputer
 			int n;
 			consumer.notifyStartSCC();
 			do {
-				n = stack.remove(0);
+				n = stack.pop();
 				onStack.set(n, false);
 				consumer.notifyStateInSCC(n);
 			} while (n != i);