回溯问题，要么取队首要么取队尾 public class Z8 { public static int solution(int[] arr, int n, int i, int max, boolean[] visit) { if (i == n) { return max; } // 取队首元素 int start = 0; for (int j = 0; j < arr.length; j++) { if (!visit[j]) { start = j; } } visit[start] = true; int max1 = solution(arr, n, i +1, max + arr[start], visit); visit[start] = false; // 取队尾元素 int end = arr.length - 1; for (int j = arr.length - 1; j >= 0; j--) { if (!visit[j]) { end = j ; } } visit[end] = true; int max2 = solution(arr, n, i +1, max + arr[end], visit); visit[end] = false; return Math.max(max1, max2); } public static void main(String[] args) { Scanner sc = new Scanner(System.in); int m = sc.nextInt(); int[] arr = new int[m]; for (int i = 0; i < m; i++) { arr[i] = sc.nextInt(); } int n = sc.nextInt(); boolean[] visit = new boolean[m]; System.out.println(solution(arr, n, 0, 0, visit)); } }