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| #define DEBUG 0
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| #include <algorithm>
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| #include <functional>
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| #include <numeric>
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| #include <iostream>
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| #include <iomanip>
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| #include <cstdio>
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| #include <cmath>
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| #include <complex>
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| #include <cstdlib>
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| #include <ctime>
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| #include <cstring>
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| #include <cassert>
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| #include <string>
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| #include <vector>
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| #include <list>
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| #include <map>
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| #include <set>
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| #include <deque>
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| #include <queue>
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| #include <stack>
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| #include <bitset>
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| #include <sstream>
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| using namespace std;
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|
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| #define LL long long
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| #define LD long double
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| #define PR pair<int,int>
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|
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| #define Fox(i,n) for (i=0; i<n; i++)
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| #define Fox1(i,n) for (i=1; i<=n; i++)
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| #define FoxI(i,a,b) for (i=a; i<=b; i++)
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| #define FoxR(i,n) for (i=(n)-1; i>=0; i--)
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| #define FoxR1(i,n) for (i=n; i>0; i--)
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| #define FoxRI(i,a,b) for (i=b; i>=a; i--)
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| #define Foxen(i,s) for (i=s.begin(); i!=s.end(); i++)
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| #define Min(a,b) a=min(a,b)
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| #define Max(a,b) a=max(a,b)
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| #define Sz(s) int((s).size())
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| #define All(s) (s).begin(),(s).end()
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| #define Fill(s,v) memset(s,v,sizeof(s))
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| #define pb push_back
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| #define mp make_pair
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| #define x first
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| #define y second
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| template<typename T> T Abs(T x) { return(x<0 ? -x : x); }
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| template<typename T> T Sqr(T x) { return(x*x); }
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| string plural(string s) { return(Sz(s) && s[Sz(s)-1]=='x' ? s+"en" : s+"s"); }
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| const int INF = (int)1e9;
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| const LD EPS = 1e-12;
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| const LD PI = acos(-1.0);
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| #if DEBUG
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| #define GETCHAR getchar
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| #else
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| #define GETCHAR getchar_unlocked
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| #endif
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| bool Read(int &x)
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| {
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| char c,r=0,n=0;
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| x=0;
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| for(;;)
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| {
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| c=GETCHAR();
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| if ((c<0) && (!r))
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| return(0);
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| if ((c=='-') && (!r))
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| n=1;
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| else
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| if ((c>='0') && (c<='9'))
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| x=x*10+c-'0',r=1;
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| else
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| if (r)
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| break;
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| }
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| if (n)
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| x=-x;
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| return(1);
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| }
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| #define LIM 6001
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| #define MOD 1000000007
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| int N,K;
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| int expMem[LIM];
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| int Exp(int a,int b)
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| {
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| if ((a<N) && (b==K) && (expMem[a]))
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| return(expMem[a]);
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| LL p=a,v=1;
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| while (b)
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| {
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| if (b&1)
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| v=v*p%MOD;
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| p=p*p%MOD;
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| b>>=1;
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| }
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| if ((a<N) && (b==K))
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| expMem[a]=v;
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| return(v);
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| }
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| void Add(int &a,int b)
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| {
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| a=(a+b)%MOD;
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| }
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| int Prod(int a,int b)
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| {
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| return((LL)a*b%MOD);
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| }
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| void Div(int &a,int b)
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| {
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| a=Prod(a,Exp(b,MOD-2));
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| }
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| int Count(int f,int r)
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| {
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| int v=N-f-1;
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| int c=Exp(v,K);
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| if (!r)
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| return(c);
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| if (r==1)
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| return((c-Exp(v-1,K)+MOD)%MOD);
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| return((c-(LL)2*Exp(v-1,K)%MOD+Exp(v-2,K)+MOD)%MOD);
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| }
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|
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| int main()
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| {
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| if (DEBUG)
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| freopen("in.txt","r",stdin);
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| int T,t;
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| int L,A,B;
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| int i,dA,dB,dL;
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| int P[LIM]={-1};
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| Read(T);
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| Fox1(t,T)
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| {
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| Fill(expMem,0);
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| Read(N),Read(K),Read(A),Read(B),A--,B--;
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| Fox1(i,N-1)
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| Read(P[i]),P[i]--;
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| queue<int> qA,qB;
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| for (dA=0; A>=0; A=P[A],dA++)
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| qA.push(A);
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| for (dB=0; B>=0; B=P[B],dB++)
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| qB.push(B);
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| dL=max(dA,dB);
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| for(;;)
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| {
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| if (qA.front()==qB.front())
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| break;
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| dL--;
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| if (Sz(qA)>dL)
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| qA.pop();
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| if (Sz(qB)>dL)
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| qB.pop();
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| }
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| dL--,dA--,dB--;
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| int ans=0;
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| if (!dL)
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| {
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| Fox(A,dA+1)
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| Fox(B,dB+1)
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| {
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| if ((dA) && (!A) || (dB) && (!B))
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| continue;
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| Add(ans,Prod(A+B,Count(A+B-(A?1:0)-(B?1:0),(A<dA?1:0)+(B<dB?1:0))));
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| }
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| }
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| else
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| {
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| Fox1(L,dL)
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| Add(ans,Prod(dA+dB-2*dL,Count(dA+dB-2*dL+L-1,(L<dL ? 1 : 0))));
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| Fox1(A,dA)
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| Fox1(B,dB)
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| {
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| if ((A>dA-dL) && (B>dB-dL))
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| continue;
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| Add(ans,Prod(A+B,Count(A+B-2,(A<dA?1:0)+(B<dB?1:0))));
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| }
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| }
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| Div(ans,Exp(N-1,K));
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| printf("Case #%d: %d\n",t,ans);
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| }
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| return(0);
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| } |
