[20250903] BOJ / G4 / 도시 분할 계획 / 김민진

zinnnn37/202509/3 BOJ G4 도시 분할 계획.md

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+```java
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.util.List;
+import java.util.PriorityQueue;
+import java.util.Queue;
+import java.util.StringTokenizer;
+
+public class BJ_1647_도시_분할_계획 {
+
+	private static final BufferedReader  br = new BufferedReader(new InputStreamReader(System.in));
+	private static       StringTokenizer st;
+
+	private static int N; // node
+	private static int M; // edge
+	private static int cnt;
+	private static int ans;
+
+	private static int[] parents;
+
+	private static Queue<Node>  pq;
+	private static List<Node>[] graph;
+
+	private static class Node implements Comparable<Node> {
+		int from;
+		int to;
+		int weight;
+
+		public Node(int from, int to, int weight) {
+			this.from   = from;
+			this.to     = to;
+			this.weight = weight;
+		}
+
+		@Override
+		public int compareTo(Node o) {
+			return Integer.compare(this.weight, o.weight);
+		}
+	}
+
+	private static StringTokenizer tokenize() throws IOException {
+		return new StringTokenizer(br.readLine());
+	}
+
+	private static int nextInt() {
+		return Integer.parseInt(st.nextToken());
+	}
+
+	public static void main(String[] args) throws IOException {
+		init();
+		sol();
+	}
+
+	private static void init() throws IOException {
+		st = tokenize();
+
+		N   = nextInt();
+		M   = nextInt();
+		cnt = 0;
+		ans = 0;
+
+		pq = new PriorityQueue<>();
+		while (M-- > 0) {
+			st = tokenize();
+
+			int a = nextInt();
+			int b = nextInt();
+			int c = nextInt();
+
+			pq.add(new Node(a, b, c));
+		}
+
+		parents = new int[N + 1];
+		for (int i = 1; i <= N; i++) {
+			parents[i] = i;
+		}
+	}
+
+	private static void sol() {
+		while (!pq.isEmpty() && cnt < N - 2) {
+			Node cur = pq.poll();
+
+			if (find(cur.from) == find(cur.to)) {
+				continue;
+			}
+			union(cur.from, cur.to);
+			cnt++;
+			ans += cur.weight;
+		}
+		System.out.println(ans);
+	}
+
+	private static void union(int a, int b) {
+		int rootA = find(a);
+		int rootB = find(b);
+
+		if (rootA < rootB) {
+			parents[rootB] = rootA;
+		} else {
+			parents[rootA] = rootB;
+		}
+	}
+
+	private static int find(int a) {
+		if (parents[a] == a) {
+			return a;
+		}
+		return parents[a] = find(parents[a]);
+	}
+
+}
+```