JavaScript: Create an array of prefix sums of the given array

JavaScript Basic: Exercise-131 with Solution

Write a JavaScript program to create an array of prefix sums of the given array.

In computer science, the prefix sum, cumulative sum, inclusive scan, or simply scan of a sequence of numbers x0, x1, x2, ... is a second sequence of numbers y0, y1, y2, ..., the sums of prefixes of the input sequence:
y0 = x0
y1 = x0 + x1
y2 = x0 + x1+ x2
...

Sample Solution:

JavaScript Code:

// Function to compute prefix sums of an array
function prefix_sums(arr) {
  var new_arr = []; // Initialize an empty array to store prefix sums
  
  // Loop through the input array
  for (var i = 0; i < arr.length; i++) {
    new_arr[i] = 0; // Initialize each element in the new array to 0
    
    // Compute the prefix sum up to index 'i' in the input array
    for (var j = 0; j < i + 1; j++) {
      new_arr[i] += arr[j]; // Sum the elements from index 0 to 'i'
    }
  }
  
  return new_arr; // Return the array containing prefix sums
}

// Test cases
console.log(prefix_sums([1, 2, 3, 4, 5])); // Output: [1, 3, 6, 10, 15]

console.log(prefix_sums([1, 2, -3, 4, 5])); // Output: [1, 3, 0, 4, 9]

Output:

[1,3,6,10,15]
[1,3,0,4,9]

Live Demo:

See the Pen javascript-basic-exercise-131 by w3resource (@w3resource) on CodePen.

Flowchart:

ES6 Version:

// Function to compute prefix sums of an array
const prefix_sums = (arr) => {
  const new_arr = []; // Initialize an empty array to store prefix sums
  	
  // Loop through the input array
  for (let i = 0; i < arr.length; i++) {
    new_arr[i] = 0; // Initialize each element in the new array to 0
    
    // Compute the prefix sum up to index 'i' in the input array
    for (let j = 0; j < i + 1; j++) {
      new_arr[i] += arr[j]; // Sum the elements from index 0 to 'i'
    }
  }
  
  return new_arr; // Return the array containing prefix sums
}

// Test cases
console.log(prefix_sums([1, 2, 3, 4, 5])); // Output: [1, 3, 6, 10, 15]

console.log(prefix_sums([1, 2, -3, 4, 5])); // Output: [1, 3, 0, 4, 9]

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