[20250923] BOJ / G3 / 두 단계 최단 경로 2 / 이강현

Author: lkhyun

lkhyun/202509/23 BOJ G3 두 단계 최단 경로 2.md

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+```java
+import java.util.*;
+import java.io.*;
+
+public class Main{
+    static class Edge{
+        int to;
+        long weight;
+        Edge(int to, long weight){
+            this.to = to;
+            this.weight = weight;
+        }
+    }
+    static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+    static BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
+    static StringTokenizer st;
+    static StringBuilder sb = new StringBuilder();
+    static int N,M;
+    static List<Edge>[] adjEdges;
+    static int X,Z;
+    static int P;
+    static long[] distStart;
+    static long[] distEnd;
+
+    public static void main(String[] args) throws Exception {
+        st = new StringTokenizer(br.readLine());
+        N = Integer.parseInt(st.nextToken());
+        M = Integer.parseInt(st.nextToken());
+
+        adjEdges = new List[N+1];
+        for (int i = 1; i <= N; i++) {
+            adjEdges[i] = new ArrayList<>();
+        }
+
+        distStart = new long[N+1];
+        distEnd = new long[N+1];
+
+        for (int i = 0; i < M; i++) {
+            st = new StringTokenizer(br.readLine());
+            int from = Integer.parseInt(st.nextToken());
+            int to = Integer.parseInt(st.nextToken());
+            long weight = Long.parseLong(st.nextToken());
+
+            adjEdges[from].add(new Edge(to, weight));
+            adjEdges[to].add(new Edge(from, weight));
+        }
+
+        st = new StringTokenizer(br.readLine());
+        X = Integer.parseInt(st.nextToken());
+        Z = Integer.parseInt(st.nextToken());
+
+        P = Integer.parseInt(br.readLine());
+        List<Integer> middleVertex = new ArrayList<>(P);
+        
+        st = new StringTokenizer(br.readLine());
+        for (int i = 0; i < P; i++) {
+            middleVertex.add(Integer.parseInt(st.nextToken()));
+        }
+
+        dijkstra(X, distStart);
+        dijkstra(Z, distEnd);
+
+        long min = Long.MAX_VALUE;
+        for (int Y : middleVertex) {
+            if(distStart[Y] == Long.MAX_VALUE || distEnd[Y] == Long.MAX_VALUE) continue;  // Integer -> Long
+            min = Math.min(min, distStart[Y] + distEnd[Y]);
+        }
+        if(min == Long.MAX_VALUE) bw.write("-1");
+        else bw.write(min + "");
+        bw.close();
+    }
+    
+    public static void dijkstra(int start, long[] dist){
+        PriorityQueue<Edge> pq = new PriorityQueue<>((a,b) -> Long.compare(a.weight,b.weight));  // Integer -> Long
+        Arrays.fill(dist, Long.MAX_VALUE);
+
+        pq.offer(new Edge(start, 0));
+        dist[start] = 0;
+        
+        while(!pq.isEmpty()){
+            Edge cur = pq.poll();
+
+            if(dist[cur.to] < cur.weight) continue;
+
+            for (Edge next : adjEdges[cur.to]) {
+                long newDistance = cur.weight + next.weight;
+                if(newDistance < dist[next.to]){
+                    dist[next.to] = newDistance;
+                    pq.offer(new Edge(next.to, newDistance));
+                }
+            }
+        }
+    }
+}
+```