[백준] 11054 - 가장 긴 바이토닉 부분 수열 [JAVA]

 

코드 (Top-down)

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;
import java.util.StringTokenizer;

public class Main {

    static int[] R_dp; // 오름 차순
    static int[] L_dp; // 내림 차순

    static int[] arr;

    public static void main(String[] args) throws IOException {

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        int N = Integer.parseInt(br.readLine());

        arr = new int[N];
        L_dp = new int[N];
        R_dp = new int[N];

        StringTokenizer st = new StringTokenizer(br.readLine());
        for (int i = 0; i < N; i++) {
            arr[i] = Integer.parseInt(st.nextToken());
        }

        int max = 0;

        LIS(N);
        LDS(N);

        for (int i = 0; i < N; i++) {
            if (R_dp[i] + L_dp[i] > max) max = R_dp[i] + L_dp[i];
        }

        System.out.println(max - 1);
    }

    static void LIS(int n) {

        for (int i = 0; i < n; i++) {
            R_dp[i] = 1;
            // i 요소 이전까지 탐색
            for (int j = 0; j < i; j++) {
                if (arr[i] > arr[j] && R_dp[i] < R_dp[j] + 1) {
                    R_dp[i] = R_dp[j] + 1;
                }
            }
        }
    }

    static void LDS(int n) {

        for (int i = n - 1; i >= 0; i--) {
            L_dp[i] = 1;
            for (int j = n - 1; j > i; j--) {
                if (arr[j] < arr[i] && L_dp[i] < L_dp[j] + 1) {
                    L_dp[i] = L_dp[j] + 1;
                }
            }
        }
    }

}