CareerCup

double Year(double x1,double x2,double R){
// If I need to check data
return log(x2/x1)/log(1+R);
}

If we know the formula of compound interest then this Question is Piece of Cake. Isn't?

int noYears(double x1, double x2, double R )
{
    int n=0;
   
   while ( x1 < x2 )
  {
       n++;
       x1 = x1 + x1*R ;
  }
if( x1 == x2)
    return n; 
else
   return -1;
}

C++

int years (double &x1, double x2, double coef, int n) {

if ( x1 * coef > x2 ) {
return 0; }

int m = years(x1, x2, coef*coef, 2*n);

if ( x1 * coef < x2 ) {
x1 *= coef;
return m + n;
}
return m;
}

public static int getN(double r){
HashMap<Integer, Double> map=new HashMap();
int n=1, pn=0;
double v=(1+r), pv=1;
map.put(0, 1.0);
while(v<2){
map.put(n, v);
pn=n;
n*=2;
pv=v;
v=v*v;
}
if(v==2){
return n;
}
int c=pn;
double cv=pv;
while(n>=1){
n=pn;
pn/=2;
if(cv*map.get(pn)<2){
c+=pn;
cv*=map.get(pn);
}
else if(cv*map.get(pn)==2){
c+=pn;
return c;
}
}
return c+1;
}