Searching with Quantum Computers

int qrandom(); 
				   /* qrandom(N,r) returns a random number between 0 and (N-1) */ 
int f(); 
				   /* f(r) is an arbitrary binary function that returns 1 only  
              		      for a single value of r, for all other values of r it returns 0 */ 
quantum_main() 
{ 
   int i, r; 
   r = qrandom(N,0); 
   for(i = 0; i < eta; i++)  /* eta is a number of order <img src="http://twimgs.com/ddj/ddj/images/ddj0104b/check.gif">N */ 
   { 
      if (f(r) == 1)  invert_phase();
                           /* f(r) is evaluated within the program itself  
                           this does not need an external observation  
                           (any observation would perturb the system) */ 
      r = qrandom(N,r); 
      if (r==0)       invert_phase(); 
      r = qrandom(N,r); 
   } 
   print(r); 
} 

Figure 3: Quantum program.