[20250822] BOJ / G4 / 도시 건설 / 김수연

suyeun84/202508/22 BOJ G4 도시 건설.md

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+```java
+import java.util.*;
+import java.io.*;
+
+public class boj21924 {
+    static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+    static StringTokenizer st;
+    static void nextLine() throws Exception {st = new StringTokenizer(br.readLine());}
+    static int nextInt() {return Integer.parseInt(st.nextToken());}
+
+    static int N, M, cnt = 0;
+    static long answer;
+    static ArrayList<ArrayList<Node>> graph = new ArrayList<>();
+    static boolean[] visited;
+    public static void main(String[] args) throws Exception {
+        nextLine();
+        N = nextInt();
+        M = nextInt();
+        visited = new boolean[N+1];
+        for (int i = 0; i <= N; i++) graph.add(new ArrayList<Node>());
+        for (int i = 0; i < M; i++) {
+            nextLine();
+            int a = nextInt();
+            int b = nextInt();
+            int c = nextInt();
+            graph.get(a).add(new Node(b, c));
+            graph.get(b).add(new Node(a, c));
+            answer += c;
+        }
+        dijkstra();
+
+        if (cnt == N) System.out.println(answer);
+        else System.out.println(-1);
+    }
+
+    static void dijkstra() {
+        PriorityQueue<Node> pq = new PriorityQueue<>((o1,o2) -> o1.c-o2.c);
+        pq.offer(new Node(1, 0));
+
+        while(!pq.isEmpty()) {
+            Node cur = pq.poll();
+            if (visited[cur.v]) continue;
+            visited[cur.v] = true;
+            answer -= cur.c;
+            cnt++;
+            for (Node next : graph.get(cur.v)) {
+                if (visited[next.v]) continue;
+                pq.offer(next);
+            }
+        }
+    }
+
+    static class Node {
+        int v, c;
+        public Node(int v, int c) {
+            this.v = v;
+            this.c = c;
+        }
+    }
+}
+```