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Permutation Descent Counts(递推)
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1968: Permutation Descent Counts
Submit Page Summary Time Limit: 1 Sec Memory Limit: 128 Mb Submitted: 123 Solved: 96
Description
Given a positive integer, N, a permutation of order N is a one-to-one (and thus onto) function from the set of integers from 1 to N to itself. If p is such a function, we represent the function by a list of its values:
[ p(1) p(2) … p(N) ]
For example,
[5 6 2 4 7 1 3]
represents the function from
{ 1 … 7 }
to itself which takes 1 to 5, 2 to 6, … , 7 to 3.
For any permutation p, a descent of p is an integer k for which
p(k) > p(k+1)
. For example, the permutation
[5 6 2 4 7 1 3]
has a descent at 2
(6 > 2)
and 5
(7 > 1)
.
For permutation p,
des(p)
is the number of descents in p. For example,
des([5 6 2 4 7 1 3]) = 2
. The identity permutation is the only permutation with
des(p) = 0
. The reversing permutation with
p(k) = N+1-k
is the only permutation with
des(p) = N-1
.
The permutation descent count (PDC) for given order N and value v is the number of permutations p of order N with
des(p) = v
. For example:
PDC(3, 0) = 1 { [ 1 2 3 ] }
PDC(3, 1) = 4 { [ 1 3 2 ], [ 2 1 3 ], [ 2 3 1 ], 3 1 2 ] }
PDC(3, 2) = 1 { [ 3 2 1 ] }`
Write a program to compute the PDC for inputs N and v. To avoid having to deal with very large numbers, your answer (and your intermediate calculations) will be computed modulo
1001113
.
Input
The first line of input contains a single integer P, (1 ≤ P ≤ 1000), which is the number of data sets that follow. Each data set should be processed identically and independently.
Each data set consists of a single line of input. It contains the data set number, K, followed by the integer order, N (2 ≤ N ≤ 100), followed by an integer value, v (0 ≤ v ≤ N-1).
Output
For each data set there is a single line of output. The single output line consists of the data set number, K, followed by a single space followed by the PDC of N and v modulo 1001113 as a decimal integer.
Sample Input
4
1 3 1
2 5 2
3 8 3
4 99 50
Sample Output
1 4
2 66
3 15619
4 325091
Hint
Source
2017湖南多校第十三场
//题意:给出 n,v 求 1 -- n 的排列中,相邻的数,出现 v 次前面数比后面数大的种数。
题解:假如设 dp[i][j] 为 1 -- i 的排列,出现 j 次前面数比后面数大的情况的种数,那么
递推,有两个来源,dp[i-1][j] 和 dp[i-1][j-1] ,只要考虑 i 放置的位置即可,分清楚情况讨论清楚即可!
比赛时没想清楚唉!
# include <cstdio>
# include <cstring>
# include <cstdlib>
# include <iostream>
# include <vector>
# include <queue>
# include <stack>
# include <map>
# include <bitset>
# include <set>
# include <cmath>
# include <algorithm>
using namespace std;
#define lowbit(x) ((x)&(-x))
#define pi acos(-1.0)
#define eps 1e-8
#define MOD 1001113
#define INF 0x3f3f3f3f
#define LL long long
inline int scan() {
int x=,f=; char ch=getchar();
while(ch<''||ch>''){if(ch=='-') f=-; ch=getchar();}
while(ch>=''&&ch<=''){x=x*+ch-''; ch=getchar();}
return x*f;
}
inline void Out(int a) {
if(a<) {putchar('-'); a=-a;}
if(a>=) Out(a/);
putchar(a%+'');
}
#define MX 105
//Code begin...
int dp[MX][MX];
void Init()
{
dp[][]=;
for (int i=;i<=;i++)
{
for (int j=;j<=i-;j++)
{
dp[i][j] = dp[i-][j]*(j+)%MOD;
if (j!=)
dp[i][j] = (dp[i][j]+dp[i-][j-]*(i-j))%MOD;
}
}
}
int main()
{
Init();
int t = scan();
while (t--)
{
int c = scan();
int n = scan();
int m = scan();
printf("%d %d\n",c,dp[n][m]);
}
return ;
}
1 3 1
2 5 2
3 8 3
4 99 50
1 4
2 66
3 15619
4 325091
Hint
Source
2017湖南多校第十三场
//题意:给出 n,v 求 1 -- n 的排列中,相邻的数,出现 v 次前面数比后面数大的种数。
题解:假如设 dp[i][j] 为 1 -- i 的排列,出现 j 次前面数比后面数大的情况的种数,那么
递推,有两个来源,dp[i-1][j] 和 dp[i-1][j-1] ,只要考虑 i 放置的位置即可,分清楚情况讨论清楚即可!
比赛时没想清楚唉!
# include <cstdio>
# include <cstring>
# include <cstdlib>
# include <iostream>
# include <vector>
# include <queue>
# include <stack>
# include <map>
# include <bitset>
# include <set>
# include <cmath>
# include <algorithm>
using namespace std;
#define lowbit(x) ((x)&(-x))
#define pi acos(-1.0)
#define eps 1e-8
#define MOD 1001113
#define INF 0x3f3f3f3f
#define LL long long
inline int scan() {
int x=,f=; char ch=getchar();
while(ch<''||ch>''){if(ch=='-') f=-; ch=getchar();}
while(ch>=''&&ch<=''){x=x*+ch-''; ch=getchar();}
return x*f;
}
inline void Out(int a) {
if(a<) {putchar('-'); a=-a;}
if(a>=) Out(a/);
putchar(a%+'');
}
#define MX 105
//Code begin...
int dp[MX][MX];
void Init()
{
dp[][]=;
for (int i=;i<=;i++)
{
for (int j=;j<=i-;j++)
{
dp[i][j] = dp[i-][j]*(j+)%MOD;
if (j!=)
dp[i][j] = (dp[i][j]+dp[i-][j-]*(i-j))%MOD;
}
}
}
int main()
{
Init();
int t = scan();
while (t--)
{
int c = scan();
int n = scan();
int m = scan();
printf("%d %d\n",c,dp[n][m]);
}
return ;
}
Source
2017湖南多校第十三场
//题意:给出 n,v 求 1 -- n 的排列中,相邻的数,出现 v 次前面数比后面数大的种数。
题解:假如设 dp[i][j] 为 1 -- i 的排列,出现 j 次前面数比后面数大的情况的种数,那么
递推,有两个来源,dp[i-1][j] 和 dp[i-1][j-1] ,只要考虑 i 放置的位置即可,分清楚情况讨论清楚即可!
比赛时没想清楚唉!
# include <cstdio>
# include <cstring>
# include <cstdlib>
# include <iostream>
# include <vector>
# include <queue>
# include <stack>
# include <map>
# include <bitset>
# include <set>
# include <cmath>
# include <algorithm>
using namespace std;
#define lowbit(x) ((x)&(-x))
#define pi acos(-1.0)
#define eps 1e-8
#define MOD 1001113
#define INF 0x3f3f3f3f
#define LL long long
inline int scan() {
int x=,f=; char ch=getchar();
while(ch<''||ch>''){if(ch=='-') f=-; ch=getchar();}
while(ch>=''&&ch<=''){x=x*+ch-''; ch=getchar();}
return x*f;
}
inline void Out(int a) {
if(a<) {putchar('-'); a=-a;}
if(a>=) Out(a/);
putchar(a%+'');
}
#define MX 105
//Code begin...
int dp[MX][MX]; void Init()
{
dp[][]=;
for (int i=;i<=;i++)
{
for (int j=;j<=i-;j++)
{
dp[i][j] = dp[i-][j]*(j+)%MOD;
if (j!=)
dp[i][j] = (dp[i][j]+dp[i-][j-]*(i-j))%MOD;
}
}
} int main()
{
Init();
int t = scan();
while (t--)
{
int c = scan();
int n = scan();
int m = scan();
printf("%d %d\n",c,dp[n][m]);
}
return ;
}








