[20250813] BOJ / D5 / Cat Exercise / 권혁준

Author: oncsr

khj20006/202508/13 BOJ D5 Cat Exercise.md

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+```java
+import java.util.*;
+import java.io.*;
+
+class IOController {
+	BufferedReader br;
+	BufferedWriter bw;
+	StringTokenizer st;
+
+	public IOController() {
+		br = new BufferedReader(new InputStreamReader(System.in));
+		bw = new BufferedWriter(new OutputStreamWriter(System.out));
+		st = new StringTokenizer("");
+	}
+
+	String nextLine() throws Exception {
+		String line = br.readLine();
+		st = new StringTokenizer(line);
+		return line;
+	}
+
+	String nextToken() throws Exception {
+		while (!st.hasMoreTokens()) nextLine();
+		return st.nextToken();
+	}
+
+	int nextInt() throws Exception {
+		return Integer.parseInt(nextToken());
+	}
+
+	long nextLong() throws Exception {
+		return Long.parseLong(nextToken());
+	}
+
+	double nextDouble() throws Exception {
+		return Double.parseDouble(nextToken());
+	}
+
+	void close() throws Exception {
+		bw.flush();
+		bw.close();
+	}
+
+	void write(String content) throws Exception {
+		bw.write(content);
+	}
+
+}
+
+public class Main {
+
+	static IOController io;
+
+	//
+
+	static int N;
+	static int[] p;
+	static long[] s;
+	static int[] r;
+	static int[][] par;
+	static int[] dep;
+	static List<Integer>[] graph;
+	static List<int[]> edges;
+
+	static int f(int x) {return x==r[x] ? x : (r[x]=f(r[x]));}
+
+	public static void main(String[] args) throws Exception {
+
+		io = new IOController();
+
+		init();
+		solve();
+
+		io.close();
+
+	}
+
+	static void init() throws Exception {
+
+		N = io.nextInt();
+		p = new int[N+1];
+		s = new long[N+1];
+		r = new int[N+1];
+		par = new int[N+1][18];
+		graph = new List[N+1];
+		dep = new int[N+1];
+		for(int i=1;i<=N;i++) {
+			p[i] = io.nextInt();
+			r[i] = i;
+			graph[i] = new ArrayList<>();
+		}
+		edges = new ArrayList<>();
+		for(int i=1;i<N;i++) {
+			int a = p[io.nextInt()];
+			int b = p[io.nextInt()];
+			edges.add(new int[]{Math.min(a,b), Math.max(a,b)});
+			graph[a].add(b);
+			graph[b].add(a);
+		}
+
+	}
+
+	static void solve() throws Exception {
+
+		dfs(N,0,0);
+		for(int k=1;k<18;k++) for(int i=1;i<=N;i++) par[i][k] = par[par[i][k-1]][k-1];
+
+		Collections.sort(edges, (a,b) -> a[1]==b[1] ? a[0]-b[0] : a[1]-b[1]);
+		for(int[] edge : edges) {
+			int a = edge[0], b = edge[1];
+			int x = f(a), y = f(b);
+			s[y] = Math.max(s[y], s[x] + dist(x, y));
+			r[x] = y;
+		}
+		io.write(s[N] + "\n");
+
+	}
+
+	static void dfs(int n, int p, int d) {
+		par[n][0] = p;
+		dep[n] = d;
+		for(int i:graph[n]) if(i != p) dfs(i,n,d+1);
+	}
+
+	static int dist(int a, int b) {
+		int diff = Math.abs(dep[a]-dep[b]);
+		int res = 0;
+		for(int k=0;k<18;k++) if((diff & (1<<k)) != 0) {
+			if(dep[a] > dep[b]) a = par[a][k];
+			else b = par[b][k];
+			res += (1<<k);
+		}
+
+		for(int k=17;k>=0;k--) if(par[a][k] != par[b][k]) {
+			res += (1<<(k+1));
+			a = par[a][k];
+			b = par[b][k];
+		}
+		if(a != b) res += 2;
+		return res;
+	}
+
+}
+```