Merge pull request #486 from AlgorithmWithGod/JHLEE325

[20250717] BOJ / G4 / 특정한 최단 경로 / 이준희

Author: ShinHeeEul

JHLEE325/202507/17 BOJ G4 특정한 최단 경로.md

@@ -0,0 +1,91 @@
+```java
+import java.io.BufferedReader;
+import java.io.InputStreamReader;
+import java.util.*;
+
+public class Main {
+    static int n, e;
+    static List<List<Node>> list = new ArrayList<>();
+    static final int INF = 987654321;
+
+    public static void main(String[] args) throws Exception {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        StringTokenizer st = new StringTokenizer(br.readLine());
+
+        n = Integer.parseInt(st.nextToken());
+        e = Integer.parseInt(st.nextToken());
+
+        for (int i = 0; i <= n; i++)
+            list.add(new ArrayList<>());
+
+        for (int i = 0; i < e; i++) {
+            st = new StringTokenizer(br.readLine());
+            int from = Integer.parseInt(st.nextToken());
+            int to = Integer.parseInt(st.nextToken());
+            int cost = Integer.parseInt(st.nextToken());
+            list.get(from).add(new Node(to, cost));
+            list.get(to).add(new Node(from, cost));
+        }
+
+        st = new StringTokenizer(br.readLine());
+        int v1 = Integer.parseInt(st.nextToken());
+        int v2 = Integer.parseInt(st.nextToken());
+
+        int[] dist1 = dijkstra(1);
+        int[] distv1 = dijkstra(v1);
+        int[] distv2 = dijkstra(v2);
+
+        int path1 = dist1[v1] + distv1[v2] + distv2[n];
+        int path2 = dist1[v2] + distv2[v1] + distv1[n];
+
+        if (dist1[v1] >= INF || distv1[v2] >= INF || distv2[n] >= INF) path1 = INF;
+        if (dist1[v2] >= INF || distv2[v1] >= INF || distv1[n] >= INF) path2 = INF;
+
+        int result = Math.min(path1, path2);
+
+        if (result >= INF)
+            System.out.println("-1");
+        else System.out.println(result);
+    }
+
+    static int[] dijkstra(int start) {
+        int[] dist = new int[n + 1];
+        Arrays.fill(dist, INF);
+        dist[start] = 0;
+
+        PriorityQueue<Node> pq = new PriorityQueue<>();
+        pq.offer(new Node(start, 0));
+
+        while (!pq.isEmpty()) {
+            Node cur = pq.poll();
+            int now = cur.idx;
+
+            if (cur.cost > dist[now]) continue;
+
+            for (Node next : list.get(now)) {
+                if (dist[next.idx] > dist[now] + next.cost) {
+                    dist[next.idx] = dist[now] + next.cost;
+                    pq.offer(new Node(next.idx, dist[next.idx]));
+                }
+            }
+        }
+
+        return dist;
+    }
+
+    public static class Node implements Comparable<Node> {
+        int idx, cost;
+
+        Node(int idx, int cost) {
+            this.idx = idx;
+            this.cost = cost;
+        }
+
+        @Override
+        public int compareTo(Node o) {
+            return Integer.compare(this.cost, o.cost);
+        }
+    }
+}
+
+```