题目传送门
1 /*
2 DFS: 排序后一个一个出发往后找，找到>r为止，比赛写了return ；
3 */
4 #include <cstdio>
5 #include <iostream>
6 #include <cstring>
7 #include <cmath>
8 #include <algorithm>
9 #include <vector>
10 #include <map>
11 #include <queue>
12 #include <set>
13 #include <string>
14 #include <stack>
15 using namespace std;
16
17 typedef long long ll;
18 const int MAXN = 1e4 + 10;
19 const int INF = 0x3f3f3f3f;
20 int a[20];
21 bool vis[20];
22 int n, l, r, x;
23 int ans;
24
25 void DFS(int sum, int cnt, int s, int p)
26 {
27 if (sum >= l && cnt >= 2 && a[p] - a[s] >= x) ans++;
28 for (int i=p+1; i<=n; ++i)
29 {
30 if (sum + a[i] <= r) DFS (sum + a[i], cnt + 1, s, i);
31 }
32 }
33
34 int main(void) //Codeforces Round #306 (Div. 2) B. Preparing Olympiad
35 {
36 while (scanf ("%d%d%d%d", &n, &l, &r, &x) == 4)
37 {
38 ans = 0;
39 for (int i=1; i<=n; ++i) scanf ("%d", &a[i]);
40 sort (a+1, a+1+n);
41 for (int i=1; i<n; ++i) DFS (a[i], 1, i, i);
42 printf ("%d
", ans);
43 }
44
45 return 0;
46 }
47
48 /*
49 3 5 6 1
50 1 2 3
51 4 40 50 10
52 10 20 30 25
53 5 25 35 10
54 10 10 20 10 20
55 */