[20260223] BOJ / G4 / 도시 건설 / 이인희

LiiNi-coder/202602/23 BOJ 도시 건설.md

@@ -0,0 +1,62 @@
+```java
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.PriorityQueue;
+
+public class Main{
+	// 크루스칼 -> 간선 중심 -> 간선이 적을때 쓰면 좋음 -> disjoint set알고리즘 구현 필요
+	// 프림 -> 정점 중심 -> MST와 우선숭위큐에 정점을 넣어가며 그 예비 MST의 간선을 선택해나가는것
+	static int N, M;
+	static List<List<int[]>> Graph;
+	public static void main(String[] args) throws IOException {
+		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+		String[] tokens = br.readLine().split(" ");
+		N = Integer.parseInt(tokens[0]);
+		M = Integer.parseInt(tokens[1]);
+		int m = M;
+		Graph = new ArrayList<>();
+		for(int i = 0; i <= N; i++){
+			Graph.add(new ArrayList<>());
+		}
+		long overSum = 0L;
+		while(m-->0){
+			tokens = br.readLine().split(" ");
+			int s = Integer.parseInt(tokens[0]);
+			int e = Integer.parseInt(tokens[1]);
+			int w = Integer.parseInt(tokens[2]);
+			overSum += w;
+			Graph.get(s).add(new int[]{e, w});
+			Graph.get(e).add(new int[]{s, w});
+		}
+
+		boolean[] visited = new boolean[N+1];
+		var q = new PriorityQueue<int[]>((o1, o2)->o1[1] - o2[1]);
+		q.add(new int[]{1, 0});
+		long mstSum = 0L;
+
+		while(!q.isEmpty()){
+			var qItem = q.poll();
+			int v = qItem[0]; int w = qItem[1];
+			if(visited[v]) continue;
+			visited[v] = true;
+			mstSum += w;
+			for(int[] nextInfo : Graph.get(v)){
+				int nv = nextInfo[0]; int nw = nextInfo[1];
+				if(visited[nv]) continue;
+				q.add(new int[]{nv, nw});
+			}
+		}
+		for(int i = 1; i < N+1; i++){
+			if(!visited[i]){
+				System.out.println(-1);
+				return;
+			}
+		}
+		System.out.println(overSum - mstSum);
+		br.close();
+	}
+}
+```