Submission #1686260

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Source Code Expand

#include<iostream>
#include<vector>
#include<algorithm>
#include<cstring>
#include<cstdio>
#include<cmath>
#include<cstdlib>
#include<ctime>
#include<queue>
#include<set>
#include<map>
#include<stack>
#include<bitset>
using namespace std;
typedef long long LL;
int gi() {
	int w=0;bool q=1;char c=getchar();
	while ((c<'0'||c>'9') && c!='-') c=getchar();
	if (c=='-') q=0,c=getchar();
	while (c>='0'&&c <= '9') w=w*10+c-'0',c=getchar();
	return q? w:-w;
}
const int N=110;
int f[N][N][N],a[N];
#define mod 1000000007
inline void inc(int &x,int y) { (x+=y)>=mod?x-=mod:0; }
int main()
{
	int n=gi(),i,j,k,t,x,y;
	for (i=1;i<n*2;i++) a[i]=gi();
	sort(a+1,a+n*2);
	f[n][1][1]=1;
	for (i=n;i;i--) {
		x=a[i]!=a[i-1];
		y=a[n*2-i+1]!=a[n*2-i];
		for (j=1;j<2*n;j++)
			for (k=1;k<=j;k++)
				if (f[i][j][k]) {
					for (t=1;t<k+x;t++)
						inc(f[i-1][j+x+y-(k+x-t-1)][t],f[i][j][k]);
					for (t=k+x+1;t<=j+x+y;t++)
						inc(f[i-1][j+x+y-(t-(k+x)-1)][k+x+1],f[i][j][k]);
					inc(f[i-1][j+x+y][k+x],f[i][j][k]);
				}
	}
	x=0;
	for (j=1;j<n*2;j++)
		for (k=1;k<=j;k++)
			inc(x,f[1][j][k]);
	printf("%d\n",x);
	return 0;
}

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