Replace Loops using Recursion

Recursion is the concept that a function can be expressed in terms of itself. To help understand this, start by thinking about the following task: Add the first n elements of an array to create the product of those elements. we can rewrite sum in terms…


This content originally appeared on DEV Community and was authored by Randy Rivera

Recursion is the concept that a function can be expressed in terms of itself. To help understand this, start by thinking about the following task: Add the first n elements of an array to create the product of those elements. we can rewrite sum in terms of itself and never need to use a loop.

  • Here we write a recursive function, sum(arr, n), that returns the sum of the first n elements of an array arr.
  • Note: Recursive functions must have a base case when they return without calling the function again (in this example, when n <= 0), otherwise they can never finish executing. 
function sum(arr, n) {
if (n <= 0) {
  return 0;
} else {
  return sum(arr, n - 1) + arr[n - 1];
}
}

console.log(sum([2, 3, 4, 5], 3)); will display 9

// sum([2, 3, 4, 5], 3 - 1) + arr[3 - 1];
// sum([2, 3, 4 ,5], 2) + arr[2];
// sum([2, 3, 4, 5], 2) + 4;
//        n = 2

// sum([2, 3, 4, 5], 2 - 1) + arr[2 - 1];
// sum([2, 3, 4, 5], 1) + arr[1];
// sum([2, 3, 4, 5], 1) + 3; 
//      n = 1             3

// sum([2, 3, 4, 5], 1 - 1) + arr[1 - 1];
// sum([2  3, 4, 5], 0) + arr[0];
// sum([2, 3, 4, 5], 0) + 2;
//      n = 0             2

//      we hit our base case so now n = 0

// 0 + 2 + 3 + 4 = 9
// we want it to return 9 because 4 + 3 + 2 = 9;


This content originally appeared on DEV Community and was authored by Randy Rivera


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