Problem - Two City Scheduling

A company needs to fly $2n$ people to two cities, $n$ to each city. Person $i$ costs $costs[i][0]$ to fly to city A and $costs[i][1]$ to city B. Minimize total cost. For $costs = [[10,20],[30,200],[400,50],[30,20]]$, send persons $0$ and $1$ to A, persons $2$ and $3$ to B. Total: $10 + 30 + 50 + 20 = 110$.

Think about the cost difference between sending someone to A versus B. Constraint: exactly $n$ people must go to each city.

If you send fewer than $n$ to city A, you violate the requirement. The cost array has two elements per person, representing the two choices. The greedy insight is to sort by opportunity cost, not absolute cost.