public static void main(String[] args) {        int n,k;        Scanner scanner = new Scanner(System.in);        n = scanner.nextInt();        k = scanner.nextInt();        String end = scanner.nextLine();        String line = scanner.nextLine();        int[] consume = new int[n];        char[] arr = line.toCharArray();        for(int i=0;i            consume[i] = arr[i] - 'a' + 1;        }        int now = 0;        int energy = k;        while(now+1            int x = consume[now+1]-consume[now]; if(x>0){                energy -= x;            }else{                energy += Math.abs(x);            }            if(energy                System.out.println(-1);                return;            }            now++;        }        System.out.println(energy);    }

看公式找规律，不用dfs也可以解public static void main(String[] args) {        // 2 = 2 - 1 + 1        // a1 = 2 - a0 + 1        // aj = n - j + 1        // j = ai        // a0        // a1 = n - a0 + 1        // a2 = n - a1 + 1        int n;        Scanner scanner = new Scanner(System.in);        n = scanner.nextInt(); for(int i=n;i>=1;i--){            System.out.print(i + "");        }    }