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April 23, 2021 10:48 pm GMT

How to 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 result 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]; //return sum(arr, n - 1) <-calls itself}}

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;

Original Link: https://dev.to/rthefounding/replace-loops-using-recursion-3npg

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