Tail Recursion | GeeksforGeeks

The tail recursive functions considered better than non tail recursive functions as tail-recursion can be optimized by compiler. 

Can a non-tail recursive function be written as tail-recursive to optimize it?
Consider the following function to calculate factorial of n. It is a non-tail-recursive function. Although it looks like a tail recursive at first look. If we take a closer look, we can see that the value returned by fact(n-1) is used in fact(n), so the call to fact(n-1) is not the last thing done by fact(n).

unsigned int fact(unsigned int n) {     if (n == 0) return 1;       return n*fact(n-1); }

The above function can be written as a tail recursive function. The idea is to use one more argument and accumulate the factorial value in second argument. When n reaches 0, return the accumulated value.

unsigned factTR(unsigned int n, unsigned int a)

{

    if (n == 0)  return a;

 

    return factTR(n-1, n*a);

}

// A wrapper over factTR

unsigned int fact(unsigned int n)

{

   return factTR(n, 1);

}

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