Cheapest Flights Within K Stops

class Solution {
        
    public int findCheapestPrice(int n, int[][] flights, int src, int dst, int K) {
        Map<Integer, List<int[]>> map = new HashMap<>();
        for (int[] flight: flights) {
            List<int[]> list = map.getOrDefault(flight[0], new ArrayList<>());
            list.add(flight);
            map.put(flight[0], list);
        }
        int[] memo = new int[n];
        Arrays.fill(memo, Integer.MAX_VALUE);
        if ( ! map.containsKey(src) ) {
            return -1;
        }
        int res = dfsCheapestPrice(src, 0, 0, map, memo, dst, K);
        return res == Integer.MAX_VALUE ? -1 : res;
    }
    
    private int dfsCheapestPrice(int currStopNum, int stopsTotal, int totalPrice, Map<Integer, List<int[]>> map, int[] memo, int dst, int K) 
    {
        if (memo[currStopNum] != Integer.MAX_VALUE && memo[currStopNum] < totalPrice) {
            return memo[currStopNum];
        }
        
        if (currStopNum == dst) {
            return totalPrice;
        }
        
        if (stopsTotal > K || ! map.containsKey(currStopNum) ) {
            return Integer.MAX_VALUE;
        }
        
        int res = Integer.MAX_VALUE;
        for (int[] flight: map.get(currStopNum)) {
            int tmp = dfsCheapestPrice(flight[1], stopsTotal + 1, totalPrice + flight[2], map, memo, dst, K);
            if (tmp != Integer.MAX_VALUE) {
                memo[flight[1]] = tmp;
            }
            res = Math.min(tmp, res);
        }
        
        return res;
    }
}