SRM413 ArithmeticProgression

ArithmeticProgression.cpp

#define MAX 128 

class ArithmeticProgression { 
  public: 
  double minCommonDifference(int a0, vector <int> a)  
  { 
    int N = SIZE(a); 
    if(N == 0) 
      return 0.0; 

    if(a[0] < a0) 
      return -1.0; 

    double Min = a[0] - a0; 
    double Max = Min + 1.0; 

    int i, j; 
    FOR(i, 0, MAX) 
    { 
      double Mid = (Min + Max)/2; 

      FOR(j, 0, N) 
        if(floor(a0 + (j + 1)*Mid) < a[j]) 
          break; 

      if(j < N) 
        Min = Mid; 
      else 
        Max = Mid; 
    } 

    FOR(i, 0, N) 
      if(int(floor(a0 + (i + 1)*Max)) != a[i]) 
        break; 

    if(i < N) 
      return -1.0; 

    return Max; 
  } 

   

};