[codeforces327E]Axis Walking

本文介绍了一个算法问题,探讨如何计算给定序列的幸运排列数量,这些排列的前缀和不包含任何非法元素。通过状态压缩DP的方法,文章提供了一种有效的解决方案,并附带源代码示例。

time limit per test : 3 seconds
memory limit per test : 512 megabytes

Iahub wants to meet his girlfriend Iahubina. They both live in Ox axis (the horizontal axis). Iahub lives at point 000 and Iahubina at point ddd.

Iahub has n positive integers a1,a2,...,ana_1, a_2, ..., ana1,a2,...,an. The sum of those numbers is ddd. Suppose p1,p2,...,pnp_1, p_2, ..., p_np1,p2,...,pn is a permutation of {1, 2, ..., n1, 2, ..., n1,2,...,n}. Then, let b1b1b1 = ap1a_{p1}ap1, b2b_2b2 = ap2a_{p2}ap2 and so on. The array b is called a “route”. There are n! different routes, one for each permutation ppp.

Iahub’s travel schedule is: he walks b1b_1b1 steps on Ox axis, then he makes a break in point b1b_1b1. Then, he walks b2b_2b2 more steps on Ox axis and makes a break in point b1 + b2b_1 + b_2b1+b2. Similarly, at jjj-th (1 ≤ j ≤ n)(1 ≤ j ≤ n)(1jn) time he walks bjb_jbj more steps on Ox axis and makes a break in point b1 + b2 + ... + bjb_1 + b_2 + ... + b_jb1+b2+...+bj.

Iahub is very superstitious and has kkk integers which give him bad luck. He calls a route “good” if he never makes a break in a point corresponding to one of those kkk numbers. For his own curiosity, answer how many good routes he can make, modulo 1000000007(109 + 7)1000000007 (10^9 + 7)1000000007(109+7).

Input

The first line contains an integer n(1 ≤ n ≤ 24)n (1 ≤ n ≤ 24)n(1n24). The following line contains nnn integers: a1, a2, ..., an(1 ≤ ai ≤ 109)a_1, a_2, ..., a_n (1 ≤ a_i ≤ 10^9)a1,a2,...,an(1ai109).

The third line contains integer k(0 ≤ k ≤ 2)k (0 ≤ k ≤ 2)k(0k2). The fourth line contains kkk positive integers, representing the numbers that give Iahub bad luck. Each of these numbers does not exceed 10910^9109.

Output

Output a single integer — the answer of Iahub’s dilemma modulo 1000000007(109 + 7)1000000007 (10^9 + 7)1000000007(109+7).

Examples
Input

3
2 3 5
2
5 7

Output

1

Input

3
2 2 2
2
1 3

Output

6

Note

In the first case consider six possible orderings:

[2, 3, 5]. Iahub will stop at position 2, 5 and 10. Among them, 5 is bad luck for him.
[2, 5, 3]. Iahub will stop at position 2, 7 and 10. Among them, 7 is bad luck for him.
[3, 2, 5]. He will stop at the unlucky 5.
[3, 5, 2]. This is a valid ordering.
[5, 2, 3]. He got unlucky twice (5 and 7).
[5, 3, 2]. Iahub would reject, as it sends him to position 5.

In the second case, note that it is possible that two different ways have the identical set of stopping. In fact, all six possible ways have the same stops: [2, 4, 6], so there’s no bad luck for Iahub.

题意:
对于一个序列{aia_iai},他的一个排列{bib_ibi}被称为幸运的,则bib_ibi的前缀和{sis_isi}(1&lt;=i&lt;=n)(1&lt;=i&lt;=n)(1<=i<=n)中有没有一个非法元素。给出数列{aia_iai}和kkk个非法元素,询问有多少个幸运的序列。
题解:
这题有点神仙,本来写的折半搜索,结果发现元素个数被卡了…后面写了个状压dp反而过了,就是卡时,要注意减少取模,否则会T。

	if(S&(1<<(i-1))){
		f[S] += f[S - (1<<(i-1))];
		sum += a[i];
	}
	if(sum is illegal){ // 如果sum是非法的,则这个状态直接记录为0
		f[S] = 0;
	}
#include<bits/stdc++.h>
#define ll long long
#define LiangJiaJun main
#define MOD 1000000007LL
using namespace std;
int n,k;
ll ans,sum,a[34],p[4];
ll f[1<<24];

int LiangJiaJun(){
    scanf("%d",&n);
    sum=0;
    for(int i=1;i<=n;i++){
        scanf("%lld",&a[i]);
        sum+=a[i];
    }
    scanf("%d",&k);
    for(int i=1;i<=k;i++)scanf("%lld",&p[i]);
    sort(p+1,p+k+1);
    while(k>0&&p[k]>sum)k--;
    f[0]=1;
    for(int S=1;S<(1<<n);S++){
        sum=0;
        for(int i=1;i<=n;i++){
            if(S&(1<<(i-1))){
                sum+=a[i];
                f[S]+=f[S-(1<<(i-1))];
            }
        }
        for(int i=1;i<=k;i++){
            if(sum==p[i])f[S]=0;
        }
        f[S]%=MOD;
    }
    printf("%lld\n",f[(1<<n)-1]);
    return 0;
}

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