[Java] 백준 2533번 사회망 서비스 - Dynamic Programming

https://www.acmicpc.net/problem/2533

부모 노드가 adapter인 경우와 그렇지 않은 경우를 나누어

dp[n][1], dp[n][0] 로 구분해 dp를 적용한 것이 인상깊었다.

 

import java.util.*;
import java.io.*;

public class g3_2533_adapter {
    static FastScanner fs = new FastScanner();
    static PrintWriter pw = new PrintWriter(System.out);
    static Node[] nodes;
    static int n;
    static int[][] dp;

    public static void main(String[] args) {
        n = fs.nextInt();
        nodes = new Node[n + 1];
        dp = new int[n + 1][2];
        for (int i=0;i<=n;i++) nodes[i] = new Node();
        
        for (int i=0;i<n-1;i++){
            int a = fs.nextInt(), b = fs.nextInt();
            nodes[a].linked.add(b);
            nodes[b].linked.add(a);
        }

        solve(-1, 1);

        pw.println(Math.min(dp[1][0], dp[1][1]));
        pw.close();
    }

    static void solve(int par, int chi){
        int sum = 0;
        for (Integer i : nodes[chi].linked){
            if (i != par){
                solve(chi, i);
                sum += dp[i][1];
            }
        }
        dp[chi][0] = sum;

        sum = 0;
        for (Integer i : nodes[chi].linked){
            sum += Math.min(dp[i][0], dp[i][1]);
        }
        dp[chi][1] = sum + 1;
    }

    static class Node{
        List<Integer> linked = new LinkedList<>();
    }

    // ----------input function----------

    static void sort(int[] a) {
        ArrayList<Integer> L = new ArrayList<>();
        for (int i : a)
            L.add(i);
        Collections.sort(L);
        for (int i = 0; i < a.length; i++)
            a[i] = L.get(i);
    }

    static class FastScanner {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st = new StringTokenizer("");

        String next() {
            while (!st.hasMoreTokens()) {
                try {
                    st = new StringTokenizer(br.readLine());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            return st.nextToken();
        }

        int nextInt() {
            return Integer.parseInt(next());
        }

        double nextDouble() {
            return Double.parseDouble(next());
        }

        int[] readArray(int n) {
            int[] a = new int[n];
            for (int i = 0; i < n; i++)
                a[i] = nextInt();
            return a;
        }

        long nextLong() {
            return Long.parseLong(next());
        }
    }
}