Eqs

Eqs

题目链接：http://acm.hust.edu.cn/vjudge/problem/viewProblem.action?id=15029

题意：

  给出系数a1,a2,a3,a4,a5,求出方程a1x1 ³+ a2x2 ³+ a3x3 ³+ a4x4 ³+ a5x5 ³=0 有多少个解。

样例：

Sample Input

37 29 41 43 47

Sample Output

654


分析：
   如果直接用5个for循环是会超时的，所以把方程a1x1x1x1+a2x2x2x2+a3x3x3x3+a4x4x4x4+a5x5x5x5=0
转变成-（a1x1x1x1+a2x2x2x2）=a3x3x3x3+a4x4x4x4+a5x5x5x5这样就将5层循环减少到3层循环。

#include<iostream>
#include<cstring>
#include<cmath>
using namespace std;
const int maxn=25000000;
int i,a[10],count=0,sum=0;
short b[maxn];
int x1,x2,x3,x4,x5;
int main()
{
    memset(b,0,sizeof(b));
for(i=0;i<5;i++)
   cin>>a[i];
for(x1=-50;x1<=50;x1++)
{   if(x1==0)  continue;
      for(x2=-50;x2<=50;x2++)
    {     
        if(x2==0)  continue;
        sum=-1*(a[0]*x1*x1*x1+a[1]*x2*x2*x2);
        if(sum<0)
            b[maxn+sum]++;
        else b[sum]++;
      }
}
for(x3=-50;x3<=50;x3++)
{    
   if(x3==0)  continue; 
      for(x4=-50;x4<=50;x4++)
      {
        if(x4==0)  continue;  
          for(x5=-50;x5<=50;x5++)
        {     
            if(x5==0)  continue;
         sum=a[2]*x3*x3*x3+a[3]*x4*x4*x4+a[4]*x5*x5*x5;
             if(sum<0)
                sum=maxn+sum;
              count=count+b[sum];
                }

    }
    }
cout<<count<<endl;
return 0;
}