에너지 모으기 - 16198번

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내 코드

package com.company;

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


public class Main {
    static boolean[] visited;
    static int N;
    static ArrayList<Integer> W;
    static int max = 0;

    public static void main(String[] args) throws IOException {
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        StringTokenizer st = null;

        N = Integer.parseInt(br.readLine());
        W = new ArrayList<>();

        st = new StringTokenizer(br.readLine());

        for (int i = 0; i < N; i++) {
            W.add(Integer.parseInt(st.nextToken()));
        }

        visited = new boolean[N];
        visited[0] = true;
        visited[N - 1] = true;

        for (int i = 1; i < N - 1; i++) {
            dfs(i, 0);
        }
        if (N == 3)
            max = W.get(0) * W.get(2);

        System.out.println(max);
    }

    static void dfs(int x, int sum) {
        if (visited[x]) {
            max = Math.max(sum, max);
            return;
        }

        visited[x] = true;

        int w1 = W.get(0);
        int w2 = W.get(N - 1);

        int z = 1;
        while (x - z > 0) {
            if (!visited[x - z]) {
                w1 = W.get(x - z);
                break;
            }
            z++;
        }

        z = 1;
        while (x + z < N - 1) {
            if (!visited[x + z]) {
                w2 = W.get(x + z);
                break;
            }
            z++;
        }

        sum += w1 * w2;

        for (int i = 1; i < W.size() - 1; i++) {
            if (i == x)
                continue;
            dfs(i, sum);
        }

        visited[x] = false;
    }
}