import java.util.ArrayList; import java.util.LinkedList; import java.util.List; import java.util.Scanner; /** * @author Q * @version 1.0 * Create by 2023/8/19 19:31 */ class Main { public static void main(String[] args) { Scanner sc = new Scanner(System.in); int n =sc.nextInt(); long[] arr = new long[n]; long sum = 0; for(int i =0;i<n;i++){ arr[i] = sc.nextLong(); sum+=arr[i]; } LinkedList<Integer> path = new LinkedList<>(); List<List<Integer>> ans = new ArrayList<>(); build(n, sum, 1, 0,path,ans,arr); System.out.println(ans.size()%1000000007); } private static void build(int k, long n, int startIndex, long sum,LinkedList<Integer> path,List<List<Integer>> ans,long[] arr) { if (sum > n) return; if (path.size() > k) return; if (sum == n && path.size() == k) { ans.add(new ArrayList<>(path)); return; } for(int i = 1; i <= 9; i++) { if(i==arr[path.size()]) continue; path.add(i); sum += i; build(k, n, i , sum,path,ans,arr); sum -= i; path.removeLast(); } } } 第四题用的回溯