Day4 Q3 - Add java code

Day-4/q3-Network Delay Time/namita0210--java.md

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+import java.util.*;
+
+public class NetworkDelayTime {
+    public int networkDelayTime(int[][] times, int n, int k) {
+        // Create a graph to represent the network
+        Map<Integer, List<int[]>> graph = new HashMap<>();
+        for (int[] time : times) {
+            graph.computeIfAbsent(time[0], key -> new ArrayList<>()).add(new int[]{time[1], time[2]});
+        }
+
+        // Priority queue to store nodes with their distances
+        PriorityQueue<int[]> pq = new PriorityQueue<>(Comparator.comparingInt(a -> a[1]));
+        pq.offer(new int[]{k, 0});
+
+        // Distance array to store the minimum distance from source to each node
+        int[] distance = new int[n + 1];
+        Arrays.fill(distance, Integer.MAX_VALUE);
+        distance[k] = 0;
+
+        while (!pq.isEmpty()) {
+            int[] current = pq.poll();
+            int node = current[0];
+            int time = current[1];
+
+            if (time > distance[node]) {
+                continue;
+            }
+
+            if (graph.containsKey(node)) {
+                for (int[] edge : graph.get(node)) {
+                    int neighbor = edge[0];
+                    int newTime = time + edge[1];
+
+                    if (newTime < distance[neighbor]) {
+                        distance[neighbor] = newTime;
+                        pq.offer(new int[]{neighbor, newTime});
+                    }
+                }
+            }
+        }
+
+        int maxTime = Arrays.stream(distance).max().getAsInt();
+        
+        return maxTime == Integer.MAX_VALUE ? -1 : maxTime;
+    }
+
+    public static void main(String[] args) {
+        NetworkDelayTime solution = new NetworkDelayTime();
+
+        // Example 1
+        int[][] times1 = {{2, 1, 1}, {2, 3, 1}, {3, 4, 1}};
+        int n1 = 4;
+        int k1 = 2;
+        System.out.println(solution.networkDelayTime(times1, n1, k1)); // Output: 2
+
+        // Example 2
+        int[][] times2 = {{1, 2, 1}};
+        int n2 = 2;
+        int k2 = 1;
+        System.out.println(solution.networkDelayTime(times2, n2, k2)); // Output: 1
+
+        // Example 3
+        int[][] times3 = {{1, 2, 1}};
+        int n3 = 2;
+        int k3 = 2;
+        System.out.println(solution.networkDelayTime(times3, n3, k3)); // Output: -1
+    }
+}