# UNDF: UNDF-2026-000001158
# UNDF: UNDF-2026-XXXXXXXXX
--- a/engines/tsage/core.h
+++ b/engines/tsage/core.h
@@ -835,6 +835,8 @@ class WalkRegions {
 private:
 	void loadOriginal();
 	void loadRevised();
+
+#include <unordered_set>
+
 public:
 	int _resNum;
 	RouteEnds _routeEnds;
@@ -843,7 +845,9 @@ public:
 	Common::Array<int> _idxList;
 	Common::Array<int> _idxList2;
-	Common::List<int> _disabledRegions;
+	// Changed from Common::List<int> to std::unordered_set<int> to make
+	// contains() and disableRegion() O(1) instead of O(D). The recursive
+	// calculateRestOfRoute() was calling contains(_disabledRegions, ...) on
+	// every connected region per step, producing O(D * R * depth) total work.
+	std::unordered_set<int> _disabledRegions;
 public:
 	WalkRegions() { _resNum = -1; }
--- a/engines/tsage/core.cpp
+++ b/engines/tsage/core.cpp
@@ -4302,18 +4302,18 @@ void WalkRegions::synchronize(Serializer &s) {
 	// Synchronize the list of disabled regions as a list of values terminated with a '-1'
 	int regionId = 0;
 	if (s.isLoading()) {
 		_disabledRegions.clear();

 		s.syncAsSint16LE(regionId);
 		while (regionId != -1) {
-			_disabledRegions.push_back(regionId);
+			_disabledRegions.insert(regionId);
 			s.syncAsSint16LE(regionId);
 		}
 	} else {
-		Common::List<int>::iterator i;
-		for (i = _disabledRegions.begin(); i != _disabledRegions.end(); ++i) {
-			regionId = *i;
+		for (const int id : _disabledRegions) {
+			regionId = id;
 			s.syncAsSint16LE(regionId);
 		}

 		regionId = -1;
 		s.syncAsSint16LE(regionId);
 	}
 }

@@ -4325,8 +4325,8 @@ void WalkRegions::synchronize(Serializer &s) {
 void WalkRegions::disableRegion(int regionId) {
-	if (!contains(_disabledRegions, regionId))
-		_disabledRegions.push_back(regionId);
+	_disabledRegions.insert(regionId);  // O(1); unordered_set deduplicates automatically
 }

 void WalkRegions::enableRegion(int regionId) {
-	_disabledRegions.remove(regionId);
+	_disabledRegions.erase(regionId);   // O(1)
 }
--- a/engines/tsage/core.cpp (calculateRestOfRoute change)
+++ b/engines/tsage/core.cpp
@@ -920,7 +920,7 @@ int PlayerMover::calculateRestOfRoute(int *routeList, int srcRegion, int destReg
 		// Check every connected region until we find a route to the destination (or we have no more to check).
 		int bestDistance = 31990;
 		while (((currDest = g_globals->_walkRegions._idxList[srcWalkRegion._idxListIndex + foundIndex]) != 0) && (!foundRoute)) {
 			// Only check the region if it isn't in the list of explicitly disabled regions
-			if (!contains(g_globals->_walkRegions._disabledRegions, (int)currDest)) {
+			if (g_globals->_walkRegions._disabledRegions.find((int)currDest) == g_globals->_walkRegions._disabledRegions.end()) {
 				int newDistance = calculateRestOfRoute(tempList, currDest, destRegion, foundRoute);