What is a recursive call. Which data structure is used in it?

Answer 1

Stack. Because of its LIFO (Last In First Out) property it remembers its 'caller' so knows whom to return when the function has to return. Recursion makes use of system stack for storing the return addresses of the function calls.

Every recursive function has its equivalent iterative (non-recursive) function. Even when such equivalent iterative procedures are written, explicit stack is to be used.

Answer 2

A recursive call occurs whenever a function calls itself, recursively. Recursive functions are often used when a solution requires a divide and conquer technique. In other words, each instance of the function reduces a large problem into smaller instances of the same problem, until a base case is reached. When all instances reach the base case, the large problem is fully resolved.

There is no data structure associated with recursive calls, however a recursive function makes use of the call stack to maintain the state of its local variables between recursive calls. That is, each instance works on its own discrete set of local variables, completely independent of all other instances. If there is no need to maintain the state of these variables after a recursive call, then recursion may not be the best solution to the problem (an iterative loop would likely be more efficient).

By way of an example, consider the Quick Sort algorithm which is a recursive function. This function receives the lower and upper bounds of an array which will initially be the entire array. During recursion, the lower and upper bounds will represent a subset of the array. When the subset has fewer than 2 elements, the function returns (this is the base case because you cannot sort fewer than 2 elements). If there are 2 or more elements, a pivot element is selected and the array is sorted such that elements to the left of the pivot are less than the pivot, while those to the right are greater or equal to the pivot. The pivot is then in its correct place, but the sets on either side remain unsorted (but on the correct side of the pivot). Since each of these two sets is simply a smaller version of the larger problem, two recursive calls are made, one for the left set, another for the right set. When the second recursive call returns, the function has completed its task and returns itself. Ultimately, each set goes through the same process, gradually dividing and subdividing the set until all subsets have reached the base case, at which point the entire array is sorted.

Although it would be possible to implement the Quick Sort algorithm as an iterative loop, recursion is much easier because of the need to maintain the lower and upper bound of the subset (which are received as arguments), as well as the pivot index (which is a local variable) within each instance. these variables are required in order to determine the lower and upper bound of the right subset, immediately after the left subset has been processed.

It should be noted, however, that once the right side of the array is processed, the function will immediately return. So there is no need to maintain the variable states from this particular call. Function calls, especially recursive calls, are expensive. So while recursion is required to process the left side of the array, it would be more efficient to simply modify the variables and recall the same instance of the function (known as a tail call), rather than make a recursive call for the right side of the array. And while this is more efficient, the function can be made yet more efficient by making a recursive call on the smaller of the two sets, and a tail call on the larger -- thus greatly reducing the depth of recursion.

Answer 3

In writing a program of recursion we do not need any data structure.

But the assembler uses the datastructure and it is stack.

Answer 4

Which of the data structure is used to implement recursion?

Answer 5

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Answer 6

Stacks. The computer used a built-in stack to execute recursive and normal function calls.

Answer 7

Stack.

Answer 8

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