HDU 5293(ZYB's Tree-DP)

#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<algorithm>
#include<functional>
#include<iostream>
#include<cmath>
#include<cctype>
#include<ctime>
using namespace std;
#define For(i,n) for(int i=1;i<=n;i++)
#define Fork(i,k,n) for(int i=k;i<=n;i++)
#define Rep(i,n) for(int i=0;i<n;i++)
#define ForD(i,n) for(int i=n;i;i--)
#define RepD(i,n) for(int i=n;i>=0;i--)
#define Forp(x) for(int p=Pre[x];p;p=Next[p])
#define Forpiter(x) for(int &p=iter[x];p;p=next[p])
#define Lson (x<<1)
#define Rson ((x<<1)+1)
#define MEM(a) memset(a,0,sizeof(a));
#define MEMI(a) memset(a,127,sizeof(a));
#define MEMi(a) memset(a,128,sizeof(a));
#define INF (2139062143)
#define F (100000007)
typedef long long ll;
int read()
{
int x=0,f=1; char ch=getchar();
while(!isdigit(ch)) {if (ch=='-') f=-1; ch=getchar();}
while(isdigit(ch)) { x=x*10+ch-'0'; ch=getchar();}
return x*f;
}

#define MAXN (500000+10)
#define MAXK (11)
int Pre[MAXN],Next[MAXN*2],edge[MAXN*2],siz=1;
void addedge(int u,int v){
edge[++siz]=v;
Next[siz]=Pre[u];
Pre[u]=siz;
}
void addedge2(int u,int v) {addedge(u,v),addedge(v,u);}
ll c[MAXN];

int f[MAXN];

int n,K,A,B;
int g[MAXN][MAXK];
void solve(int root)
{
Rep(i,K+1) g[root][i]=1;
Forp(root) {
int v=edge[p];
solve(v);
For(i,K) g[root][i] += g[v][i-1];
}

}
void calc(int root,int k2)
{
c[root]=g[root][k2];
int p=root;
while ((p^1) && (k2--) ) {
c[root]+=g[f[p]][k2];
if (k2) c[root]-=g[p][k2-1];

p=f[p];
}
}

int main()
{
//  freopen("D.in","r",stdin);
//  freopen(".out","w",stdout);

int T=read();
while(T--) {
n=read(),K=read(),A=read(),B=read();
For(i,n) Pre[i]=c[i]=0; siz=1;

f[1]=0;
Fork(i,2,n) {
f[i]=((ll)A*(ll)i+B)%(i-1)+1;
addedge(f[i],i);
}

solve(1);
For(i,n) calc(i,K);
ll t=0;
For(i,n) t^=c[i];
cout<<t<<endl;

}

return 0;
}