[20251019] BOJ / P3 / 교수님은 기다리지 않는다 / 김민진

zinnnn37/202510/19 BOJ P3 교수님은 기다리지 않는다.md

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+```java
+import java.io.*;
+import java.util.StringTokenizer;
+
+public class BJ_3830_교수님은_기다리지_않는다 {
+
+	private static final BufferedReader  br = new BufferedReader(new InputStreamReader(System.in));
+	private static final BufferedWriter  bw = new BufferedWriter(new OutputStreamWriter(System.out));
+	private static final StringBuilder   sb = new StringBuilder();
+	private static       StringTokenizer st;
+
+	private static int N, M;
+	private static int[] parent, weight;
+
+	public static void main(String[] args) throws IOException {
+		while (init()) {
+			sol();
+		}
+		bw.flush();
+		bw.close();
+		br.close();
+	}
+
+	private static boolean init() throws IOException {
+		st = new StringTokenizer(br.readLine());
+		N = Integer.parseInt(st.nextToken());
+		M = Integer.parseInt(st.nextToken());
+
+		if (N == 0) return false;
+
+		parent = new int[N + 1];
+		weight = new int[N + 1];
+		for (int i = 1; i <= N; i++) {
+			parent[i] = i;
+		}
+
+		return true;
+	}
+
+	private static void sol() throws IOException {
+		while (M-- > 0) {
+			st = new StringTokenizer(br.readLine());
+
+			String cmd = st.nextToken();
+
+			if (cmd.equals("!")) {
+				int a = Integer.parseInt(st.nextToken());
+				int b = Integer.parseInt(st.nextToken());
+				int w = Integer.parseInt(st.nextToken());
+
+				union(a, b, w);
+			} else if (cmd.equals("?")) {
+				int a = Integer.parseInt(st.nextToken());
+				int b = Integer.parseInt(st.nextToken());
+
+				if (find(a) == find(b)) {
+					bw.write(weight[b] - weight[a] + "\n");
+				} else {
+					bw.write("UNKNOWN\n");
+				}
+			}
+		}
+	}
+
+	private static int find(int a) {
+		if (a == parent[a]) return a;
+
+		int root = find(parent[a]);
+		weight[a] += weight[parent[a]];
+		parent[a] = root;
+
+		return root;
+	}
+
+	private static void union(int a, int b, int w) {
+		int rootA = find(a);
+		int rootB = find(b);
+
+		if (rootA == rootB) {
+			return;
+		}
+
+		if (rootA < rootB) {
+			parent[rootB] = rootA;
+			weight[rootB] = weight[a] - weight[b] + w;
+		} else {
+			parent[rootA] = rootB;
+			weight[rootA] = weight[b] - weight[a] - w;
+		}
+	}
+
+}
+```