SPOJ Triple Sums(FFT+容斥原理)
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# include <cstdio> # include <cstring> # include <cstdlib> # include <iostream> # include <vector> # include <queue> # include <stack> # include <map> # include <complex> # include <set> # include <cmath> # include <algorithm> using namespace std; # define lowbit(x) ((x)&(-x)) const double pi=acos(-1.0); # define eps 1e-8 # define MOD 1000000007 # define INF 1000000000 # define mem(a,b) memset(a,b,sizeof(a)) # define FOR(i,a,n) for(int i=a; i<=n; ++i) # define FDR(i,a,n) for(int i=a; i>=n; --i) # define bug puts("H"); # define lch p<<1,l,mid # define rch p<<1|1,mid+1,r # define mp make_pair # define pb push_back typedef pair<int,int> PII; typedef vector<int> VI; # pragma comment(linker, "/STACK:1024000000,1024000000") typedef long long LL; inline int Scan() { int x=0,f=1; char ch=getchar(); while(ch<\'0\'||ch>\'9\'){if(ch==\'-\') f=-1; ch=getchar();} while(ch>=\'0\'&&ch<=\'9\'){x=x*10+ch-\'0\'; ch=getchar();} return x*f; } inline void Out(int a) { if(a<0) {putchar(\'-\'); a=-a;} if(a>=10) Out(a/10); putchar(a%10+\'0\'); } const int N=80005; //Code begin.... typedef complex<double> cmx; int c[N<<2], val[N<<2], a[N<<2], b[N<<2]; cmx x[N<<2], y[N<<2]; void change(cmx x[], int len) { int i, j, k; for(i=1, j=len>>1; i<len-1; ++i) { if(i<j) swap(x[i],x[j]); k=len>>1; while(j>=k) j-=k, k>>=1; if(j<k) j+=k; } } void fft(cmx x[], int len, int on) { change(x,len); for(int i=2; i<=len; i<<=1) { cmx wn(cos(-on*2*pi/i),sin(-on*2*pi/i)); for(int j=0; j<len; j+=i) { cmx w(1,0); FOR(k,j,j+i/2-1) { cmx u=x[k], v=x[k+i/2]*w; x[k]=u+v; x[k+i/2]=u-v; w*=wn; } } } if(on==-1) FOR(i,0,len-1) x[i]/=len; } int main() { int n, maxx=0; cmx three(3.0,0); scanf("%d",&n); FOR(i,1,n) scanf("%d",val+i), val[i]+=20000, maxx=max(maxx,val[i]); maxx*=3; FOR(i,1,n) ++a[val[i]], ++b[val[i]*2], ++c[val[i]*3]; int len=1; while(len<maxx) len<<=1; //len要为2的幂次 FOR(i,0,len-1) x[i]=cmx(a[i],0), y[i]=cmx(b[i],0); fft(x,len,1); fft(y,len,1); //将系数表达式转化为点值表达式 FOR(i,0,len-1) x[i]=x[i]*x[i]*x[i]-x[i]*y[i]*three; fft(x,len,-1); FOR(i,0,len-1) a[i]=(int(x[i].real()+0.5)+2*c[i])/6; FOR(i,0,len-1) { if(!a[i]) continue; printf("%d : %d\\n", i-3*20000,a[i]); } return 0; }
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