How do I plan the optimal car trip visiting 4 different cities([CITY1],[CITY2],[CITY3],[CITY4])? Let's think step by step.
I would start with finding a route that minimizes total distance between all pairs of destinations, which can be done using a combination of graph algorithms and dynamic programming. You could then look at minimizing fuel consumption as well as traffic congestion. Finally you may want to consider food, entertainment or other amenities along your journey