Example 1:
Input: n = 4, flights = [[0,1,100],[1,2,100],[2,0,100],[1,3,600],[2,3,200]], src = 0, dst = 3, k = 1
Output: 700
Example 2:
Input: n = 4, flights = [[0,1,100],[1,2,100],[2,0,100],[1,3,600],[2,3,200]], src = 0, dst = 3, k = 2
Output: 400
There are n cities connected by some flights. You are given an array flights where flights[i] = [from_i, to_i, price_i] indicates a flight from city from_i to city to_i with cost price_i.
Given src, dst, and k, return the cheapest price from src to dst with at most k stops. If there is no such route, return -1.
1 <= n <= 1000 <= flights.length <= n * (n - 1) / 2flights[i].length == 30 <= from_i, to_i < n1 <= price_i <= 10^40 <= k < n