2015
05-23

# Divide Chocolate

It is well known that claire likes dessert very much, especially chocolate. But as a girl she also focuses on the intake of calories each day. To satisfy both of the two desires, claire makes a decision that each chocolate should be divided into several parts, and each time she will enjoy only one part of the chocolate. Obviously clever claire can easily accomplish the division, but she is curious about how many ways there are to divide the chocolate.

To simplify this problem, the chocolate can be seen as a rectangular contains n*2 grids (see above). And for a legal division plan, each part contains one or more grids that are connected. We say two grids are connected only if they share an edge with each other or they are both connected with a third grid that belongs to the same part. And please note, because of the amazing craft, each grid is different with others, so symmetrical division methods should be seen as different.

First line of the input contains one integer indicates the number of test cases. For each case, there is a single line containing two integers n (1<=n<=1000) and k (1<=k<=2*n).n denotes the size of the chocolate and k denotes the number of parts claire wants to divide it into.

First line of the input contains one integer indicates the number of test cases. For each case, there is a single line containing two integers n (1<=n<=1000) and k (1<=k<=2*n).n denotes the size of the chocolate and k denotes the number of parts claire wants to divide it into.

2
2 1
5 2

1
45

#include <cstring>
#include <iostream>
#include <cmath>
#include <algorithm>
#include <cstdio>
using namespace std;
#define mod 100000007
#define maxn 1010
int dp[maxn][2030][2];
int main()
{
memset(dp,0,sizeof(dp));
dp[1][1][0]=1;
dp[1][1][1]=0;
dp[1][2][1]=1;
dp[1][2][0]=0;
for(int i=2;i<maxn;i++)
{
for(int j=1;j<2*maxn;j++)
{
dp[i][j][0]=(dp[i-1][j][0]+2*dp[i-1][j][1]+dp[i-1][j-1][0]+dp[i-1][j-1][1])%mod;
if(j>=2)
dp[i][j][1]=(2*dp[i-1][j-1][0]+dp[i-1][j][1]+2*dp[i-1][j-1][1]+dp[i-1][j-2][0]+dp[i-1][j-2][1])%mod;
else
dp[i][j][1]=(2*dp[i-1][j-1][0]+dp[i-1][j][1]+2*dp[i-1][j-1][1])%mod;
}
}
int t;
scanf("%d",&t);
while(t--)
{
int n,k;
scanf("%d%d",&n,&k);
printf("%d\n",(dp[n][k][0]+dp[n][k][1])%mod);
}
return 0;
}