【codeforces 550B】Preparing Olympiad

time limit per test2 seconds
memory limit per test256 megabytes
inputstandard input
outputstandard output
You have n problems. You have estimated the difficulty of the i-th one as integer ci. Now you want to prepare a problemset for a contest, using some of the problems you’ve made.

A problemset for the contest must consist of at least two problems. You think that the total difficulty of the problems of the contest must be at least l and at most r. Also, you think that the difference between difficulties of the easiest and the hardest of the chosen problems must be at least x.

Find the number of ways to choose a problemset for the contest.

Input
The first line contains four integers n, l, r, x (1 ≤ n ≤ 15, 1 ≤ l ≤ r ≤ 109, 1 ≤ x ≤ 106) — the number of problems you have, the minimum and maximum value of total difficulty of the problemset and the minimum difference in difficulty between the hardest problem in the pack and the easiest one, respectively.

The second line contains n integers c1, c2, …, cn (1 ≤ ci ≤ 106) — the difficulty of each problem.

Output
Print the number of ways to choose a suitable problemset for the contest.

Examples
input
3 5 6 1
1 2 3
output
2
input
4 40 50 10
10 20 30 25
output
2
input
5 25 35 10
10 10 20 10 20
output
6
Note
In the first example two sets are suitable, one consisting of the second and third problem, another one consisting of all three problems.

In the second example, two sets of problems are suitable — the set of problems with difficulties 10 and 30 as well as the set of problems with difficulties 20 and 30.

In the third example any set consisting of one problem of difficulty 10 and one problem of difficulty 20 is suitable.

【题目链接】:http://codeforces.com/contest/550/problem/B

【题解】

枚举每个数是否被选;
n最大15;
复杂度O(2^n);
怎么样都不会超了
最后看看选的数字是不是符合要求就好.

【完整代码】

#include <bits/stdc++.h>
using namespace std;
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1
#define LL long long
#define rep1(i,a,b) for (int i = a;i <= b;i++)
#define rep2(i,a,b) for (int i = a;i >= b;i--)
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define rei(x) scanf("%d",&x)
#define rel(x) scanf("%I64d",&x)

typedef pair<int,int> pii;
typedef pair<LL,LL> pll;

const int MAXN = 20;
const int dx[9] = {0,1,-1,0,0,-1,-1,1,1};
const int dy[9] = {0,0,0,-1,1,-1,1,-1,1};
const double pi = acos(-1.0);

int n,l,r,x;
bool in[MAXN];
int c[MAXN];
int ans = 0;

void sear_ch(int now)
{
    if (now==n+1)
    {
        int ma = 0,mi = 1e7;
        int sum = 0;
        rep1(i,1,n)
            if (in[i])
            {
                sum += c[i];
                ma = max(ma,c[i]);
                mi = min(mi,c[i]);
            }
        if (ma-mi>=x && l <= sum && sum <= r)
            ans++;
        return;
    }
    in[now] = true;
    sear_ch(now+1);
    in[now] = false;
    sear_ch(now+1);
}

int main()
{
    //freopen("F:\rush.txt","r",stdin);
    rei(n);rei(l);rei(r);rei(x);
    rep1(i,1,n)
        rei(c[i]);
    sear_ch(1);
    printf("%d
",ans);
    return 0;
}