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Java Solution for LeetCode algorithm problems, continually updating
package g0701_0800.s0787_cheapest_flights_within_k_stops;
// #Medium #Dynamic_Programming #Depth_First_Search #Breadth_First_Search #Heap_Priority_Queue
// #Graph #Shortest_Path #2022_03_26_Time_9_ms_(53.93%)_Space_46.9_MB_(59.68%)
import java.util.Arrays;
public class Solution {
public int findCheapestPrice(int n, int[][] flights, int src, int dst, int k) {
// k + 2 becase there are total of k(intermediate stops) + 1(src) + 1(dst)
// dp[i][j] = cost to reach j using atmost i edges from src
int[][] dp = new int[k + 2][n];
for (int[] row : dp) {
Arrays.fill(row, Integer.MAX_VALUE);
}
// cost to reach src is always 0
for (int i = 0; i <= k + 1; i++) {
dp[i][src] = 0;
}
// k+1 because k stops + dst
for (int i = 1; i <= k + 1; i++) {
for (int[] flight : flights) {
int srcAirport = flight[0];
int destAirport = flight[1];
int cost = flight[2];
// if cost to reach srcAirport in i - 1 steps is already found out then
// the cost to reach destAirport will be min(cost to reach destAirport computed
// already from some other srcAirport OR cost to reach srcAirport in i - 1 steps +
// the cost to reach destAirport from srcAirport)
if (dp[i - 1][srcAirport] != Integer.MAX_VALUE) {
dp[i][destAirport] = Math.min(dp[i][destAirport], dp[i - 1][srcAirport] + cost);
}
}
}
// checking for dp[k + 1][dst] because there are 'k + 2' airports in a path and distance
// covered between 'k + 2' airports is 'k + 1'
return dp[k + 1][dst] == Integer.MAX_VALUE ? -1 : dp[k + 1][dst];
}
}