TMath::Permute

// tutorial illustrating the use of TMath::Permute
//  can be run with:
// root > .x permute.C
// root > .x permute.C+ with ACLIC

#include <TMath.h>

int permuteSimple1 () 
{
  printf("nTMath::Permute simple testn");
  printf("==========================n");
  char aa='a';
  Int_t a[4];
  Int_t i;
  Int_t icount=0;
  for(i=0; i<4; i++) a[i]=i;
  do { 
    icount++;
    for(Int_t i=0;i<4;printf("%c",static_cast<char>(aa+a[i++]))); printf("n");
  } while(TMath::Permute(4,a));
  printf("Found %d permutations = 4!n",icount);
  return 0;
}

int permuteSimple2 () 
{
  printf("nTMath::Permute simple test with repetitionn");
  printf("==========================================n");
  char aa='a'-1;
  Int_t a[6];
  Int_t i;
  Int_t icount=0;
  for(i=0; i<6; i++) a[i]=(i+2)/2;
  do { 
     icount++;
     for(Int_t i=0;i<5;printf("%c",static_cast<char>(aa+a[i++]))); printf("n");
  } while(TMath::Permute(5,a));
  printf("Found %d permutations = 5!/(2! 2!)n",icount);
  return 0;
}

Int_t permuteFancy() 
{
  Int_t a[10];
  Int_t &n=a[0], &i=a[1];
  Int_t &e=a[2], &t=a[3];
  Int_t &h=a[4], &r=a[5];
  Int_t &f=a[6], &o=a[7];
  Int_t &s=a[8], &u=a[9];
  Int_t nine, three, neuf, trois;

  printf("nTMath::Permute fancy testn");
  printf("=========================n");
  printf("This is a program to calculate the solution to the following problemn");
  printf("Find the equivalence between letters and numbers so thatn\n");
  printf("              NINE*THREE = NEUF*TROISn\n");
  for(Int_t ii=0; ii<10; ii++) a[ii]=ii;
  do {
     nine=((n*10+i)*10+n)*10+e;
     neuf=((n*10+e)*10+u)*10+f;
     three=(((t*10+h)*10+r)*10+e)*10+e;
     trois=(((t*10+r)*10+o)*10+i)*10+s;
     if(nine*three==neuf*trois) {
        printf("Solution found!n\n");
        printf("T=%d N=%d E=%d S=%d F=%d H=%d R=%d I=%d O=%d U=%dn",t,n,e,s,f,h,r,i,o,u);
        printf("NINE=%d THREE=%d NEUF=%d TROIS=%dn",nine,three,neuf,trois);
        printf("NINE*THREE = NEUF*TROIS = %dn",neuf*trois);
        return 0;
     }
  } while(TMath::Permute(10,a));
  printf("No solutions found -- something is wrong here!n");
  return 0;
}

void permute() {
   permuteSimple1();
   permuteSimple2();
   permuteFancy();
}