Tail recursion to calculate sum of array elements.

Given an array A[], we need to find the sum of its elements using Tail Recursion Method. We generally want to achieve tail recursion (a recursive function where recursive call is the last thing that function does) so that compilers can optimize the code. Basically, if recursive call is the last statement, the compiler does not need to save the state of parent call.
Examples:

Input : A[] = {1, 8, 9}
Output : 18

Input : A[] = {2, 55, 1, 7}
Output : 65

For Linear Recursion Method, refer: https://www.geeksforgeeks.org/sum-array-elements-using-recursion/

Logic: Here the key to tail recursion is whatever operation is applied with the function call, maintain it as a separate function parameter.
So, keep the sum of the last elements K elements as a function parameter and return sum when K=0.

C++

 #include using namespace std;    // Tail recursive function int arrSum(int* array, int size, int sum = 0) {     // Base Case     if (size == 0)          return sum;        // Function Call Observe sum+array[size-1]     // to maintain sum of elements     return arrSum(array, size - 1, sum + array[size - 1]); }    int main() {     int array[] = { 2, 55, 1, 7 };     int size = sizeof(array) / sizeof(array);     cout << arrSum(array, size);     return 0; }

Python3

 # Python3 implementation of the given approach.    # Tail recursive function  def arrSum(array, size, Sum = 0):         # Base Case      if size == 0:          return Sum        # Function Call Observe sum+array[size-1]      # to maintain sum of elements      return arrSum(array, size - 1,             Sum + array[size - 1])     # Driver Code if __name__ == "__main__":        array = [2, 55, 1, 7]      size = len(array)      print(arrSum(array, size))     # This code is contributed by Rituraj Jain

Output:

65

Time Complexity: O(n)

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Improved By : rituraj_jain

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