USACO-Section1.4 Arithmetic Progressions

2017-6-7

题目描述

求出满足条件的等差数列的首项和公差

解答

枚举法

代码

/*ID: 18795871PROG: ariprogLANG: C++*/#include<iostream>#include<cstdlib>#include<fstream>using namespace std;ifstream fin("ariprog.in");ofstream fout("ariprog.out");const int N=125000;bool f[N+1];struct sl{   int a,b;}x[10001];int m,n,r=0;int cmp(const void *a,const void *b){   struct sl *k1=(struct sl *)a;   struct sl *k2=(struct sl *)b;   if (k1->b==k2->b) return k1->a-k2->a;   else return k1->b-k2->b;}void init(){   int i,j;   for (i=0;i<=m;i++){       for (j=i;j<=m;j++){         f[i*i+j*j]=true;       }   }}void res(){   int i,j;   for (i=0;i<=2*m*m;i++){      if (!f[i]) continue;      for (j=1;j<=2*m*m/(n-1);j++){         if (i+j>2*m*m||!f[i+j]) continue;         if (i+j*2>2*m*m||!f[i+j*2]) continue;         if (i+j*(n-1)>2*m*m||!f[i+j*(n-1)]) continue;         int cnt=3;         while (cnt<n){            if (!f[i+cnt*j]) break;            cnt++;         }         if (cnt==n){            x[r].a=i;            x[r].b=j;            r++;         }      }   }}int main(){   fin>>n>>m;   init();   res();   if (r==0) fout<<"NONE"<<endl;   else{      qsort(x,r,sizeof(x[1]),cmp);      for (int i=0;i<r;i++){         fout<<x[i].a<<" "<<x[i].b<<endl;      }   }   return 0;}