⚡ Bolt: Optimize getTransferableLines with O(1) cache lookup

.jules/bolt.md

@@ -5,3 +5,7 @@
 ## 2024-04-15 - [Avoid O(N log N) Sorting on Massive Geographical Collections]
 **Learning:** In spatial queries like `findNearbyStations` where we scan `railwayData` containing thousands of stations to find the top K nearest points, allocating all elements to an array and running `Array.prototype.sort()` results in massive temporary object allocation and $O(N \log N)$ execution time (taking ~8.5ms in benchmarks).
 **Action:** Replace full array sorts with a bounded Top-K array using a simple $O(K)$ insertion sort during the $O(N)$ iteration phase. This brings the time complexity effectively down to $O(N)$, speeding up operations by ~36x (taking ~0.24ms). Remember to apply a final sort if total elements found are less than $K$.
+
+## 2024-05-25 - [O(1) Station Name Lookup in getTransferableLines]
+**Learning:** getTransferableLines loops over all lines and stations to match station names, taking O(L*S) time.
+**Action:** Use the existing buildStationIndex which provides an O(1) cache for station names to optimize this search.

src/core/railwayRouting.ts

@@ -50,15 +50,21 @@ export const getTransferableLines = (station: Station | undefined, currentLineKe
         });
     }
 
-    for (const lineKey in railwayData) {
-        if (!Object.prototype.hasOwnProperty.call(railwayData, lineKey)) continue;
-        if (lineKey === currentLineKey) continue;
-        if (validLines.has(lineKey)) continue;
-        const nextMeta = railwayData[lineKey].meta;
-        const sameNameStation = railwayData[lineKey].stations.find(s => s.name_ja === station.name_ja);
-        if (sameNameStation) {
-            const dist = calcDist(station.lat, station.lng, sameNameStation.lat, sameNameStation.lng);
-            if (dist < 0.5) validLines.add(lineKey);
+    // Optimize: Use O(1) station index instead of O(L*S) loop
+    const stationIndexMap = buildStationIndex(railwayData);
+    const sameNameStations = stationIndexMap.get(station.name_ja);
+
+    if (sameNameStations) {
+        for (const match of sameNameStations) {
+            const lineKey = match.lineKey;
+            if (lineKey === currentLineKey) continue;
+            if (validLines.has(lineKey)) continue;
+
+            const sameNameStation = railwayData[lineKey].stations[match.stationIndex];
+            if (sameNameStation) {
+                const dist = calcDist(station.lat, station.lng, sameNameStation.lat, sameNameStation.lng);
+                if (dist < 0.5) validLines.add(lineKey);
+            }
         }
     }
     return Array.from(validLines);