Atcoder Grand Contest 107 A Biscuits

A - Biscuits

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Time limit : 2sec / Memory limit : 256MB

Score : 200 points

Problem Statement

There are N bags of biscuits. The i-th bag contains A_i biscuits.

Takaki will select some of these bags and eat all of the biscuits inside. Here, it is also possible to select all or none of the bags.

He would like to select bags so that the total number of biscuits inside is congruent to P modulo 2. How many such ways to select bags there are?

Constraints

• 1≤N≤50
• P=0 or 1
• 1≤A_i≤100

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Input

Input is given from Standard Input in the following format:

N P
A1 A2 ... AN

Output

Print the number of ways to select bags so that the total number of biscuits inside is congruent to P modulo 2.

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Sample Input 1

2 0
1 3

Sample Output 1

2

There are two ways to select bags so that the total number of biscuits inside is congruent to 0 modulo 2:

• Select neither bag. The total number of biscuits is 0.
• Select both bags. The total number of biscuits is 4.

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Sample Input 2

1 1
50

Sample Output 2

0

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Sample Input 3

3 0
1 1 1

Sample Output 3

4

Two bags are distinguished even if they contain the same number of biscuits.

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Sample Input 4

45 1
17 55 85 55 74 20 90 67 40 70 39 89 91 50 16 24 14 43 24 66 25 9 89 71 41 16 53 13 61 15 85 72 62 67 42 26 36 66 4 87 59 91 4 25 26

Sample Output 4

17592186044416
排列组合

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <cmath>
#include <queue>
#include <stack>
#include <map>
#include <vector>
using namespace std;
typedef long long ll;
ll C(ll k,ll n)
{
    ll pos=1;
    for(ll i=0;i<k;i++)
    {
        pos*=(n-i);
        pos/=(i+1);
    }
    /*for(ll i=0;i<k;i++)
        pos/=(i+1);*/
    return pos;
}
int main()
{
    ll n,m,ans=0,pos=0,x,cnt=0;
    cin>>n>>m;
    for(ll i=1;i<=n;i++)
    {
        cin>>x;
        if(x%2==0) ans++;
        else pos++;
    }
    if(m==0)
    {
        cnt=1;
        ll nn=0,mm=0;
        for(ll i=1;i<=ans;i++)
            nn+=C(i,ans);
        for(ll i=2;i<=pos;i+=2)
            mm+=C(i,pos);
        cnt+=nn+mm+(nn*mm);
    }
    else
    {
        ll nn=0,mm=0;
        for(ll i=1;i<=ans;i++)
            nn+=C(i,ans);
        for(ll i=1;i<=pos;i+=2)
            mm+=C(i,pos);
        cnt+=(mm+(mm*nn));
    }
    cout<<cnt<<endl;
    return 0;
}

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