Tail recursion to calculate sum of array elements. - GeeksforGeeks

14 May, 2021
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++
Java
Python3
C#
Javascript
#include <bits/stdc++.h>using namespace std; // Tail recursive functionint 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[0]);    cout << arrSum(array, size);    return 0;}
// Java implementation of the given approach.class GFG{ // Tail recursive functionstatic int arrSum(int []array, int size, int sum){    // 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 codepublic static void main(String[] args){    int array[] = { 2, 55, 1, 7 };    int size = array.length;    System.out.print(arrSum(array, size, 0));}} // This code is contributed by Rajput-Ji
# Python3 implementation of the given approach. # Tail recursive functiondef 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 Codeif __name__ == "__main__":     array = [2, 55, 1, 7]    size = len(array)    print(arrSum(array, size)) # This code is contributed by Rituraj Jain
     // C# implementation of the given approach.using System; class GFG{ // Tail recursive functionstatic int arrSum(int []array, int size, int sum){    // 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 codepublic static void Main(String[] args){    int []array = { 2, 55, 1, 7 };    int size = array.Length;    Console.WriteLine(arrSum(array, size, 0));}} // This code is contributed by 29AjayKumar
<script> // Tail recursive functionfunction 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]);} var array = [2, 55, 1, 7];var size = array.length;document.write( arrSum(array, size)); </script>   
65
 
Time Complexity: O(n) 
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Practice Questions for Recursion | Set 1
Recursively Reversing a linked list (A simple implementation)
Sum of natural numbers using recursion
Count N-length strings consisting only of vowels sorted lexicographically
Count number of nodes in a complete Binary Tree
Generating subarrays using recursion
Recursive Insertion Sort
Practice Questions for Recursion | Set 2
Program to reverse a string (Iterative and Recursive)
How will you print numbers from 1 to 100 without using loop?