JavaScript Sorting Algorithm: Sorts an array of numbers, using the selection sort algorithm

JavaScript Sorting Algorithm: Exercise-5 with Solution

Selection Sort

Write a JavaScript program to sort a list of elements using the Selection sort algorithm.

The selection sort improves on the bubble sort by making only one exchange for every pass through the list.

Pictorial Presentation: Selection Sort

Sample Solution-1:

JavaScript Code:

// Selection sort with O(n^2) time complexity

function Selection_Sort(arr, compare_Function) {

  function compare(a, b) {
   return a - b;
   } 
  var min = 0;
  var index = 0;
  var temp = 0;

 //{Function} compare_Function Compare function
  compare_Function = compare_Function || compare;

  for (var i = 0; i < arr.length; i += 1) {
    index = i;
    min = arr[i];

    for (var j = i + 1; j < arr.length; j += 1) {
      if (compare_Function(min, arr[j]) > 0) {
        min = arr[j];
        index = j;
      }
    }

    temp = arr[i];
    arr[i] = min;
    arr[index] = temp;
  }

  //return sorted arr
  return arr;
}

console.log(Selection_Sort([3, 0, 2, 5, -1, 4, 1], function(a, b) { return a - b; })); 
console.log(Selection_Sort([3, 0, 2, 5, -1, 4, 1], function(a, b) { return b - a; }));

Sample Output:

[-1,0,1,2,3,4,5]
[5,4,3,2,1,0,-1]

Flowchart:

Sample Solution-2:

• Use the spread operator (...) to clone the original array, arr.
• Use a for loop to iterate over elements in the array.
• Use Array.prototype.slice() and Array.prototype.reduce() to find the index of the minimum element in the subarray to the right of the current index and perform a swap, if necessary.

JavaScript Code:

const selectionSort = arr => {
  const a = [...arr];
  for (let i = 0; i < a.length; i++) {
    const min = a
      .slice(i + 1)
      .reduce((acc, val, j) => (val < a[acc] ? j + i + 1 : acc), i);
    if (min !== i) [a[i], a[min]] = [a[min], a[i]];
  }
  return a;
};

console.log(selectionSort([5, 1, 4, 2, 3]));

Sample Output:

[1,2,3,4,5]

Flowchart:

Live Demo:

See the Pen searching-and-sorting-algorithm-exercise-5 by w3resource (@w3resource) on CodePen.

For more Practice: Solve these Related Problems:

• Write a JavaScript function that implements selection sort and returns the sorted array.
• Write a JavaScript function that sorts an array in descending order using selection sort.
• Write a JavaScript function that logs the minimum element found in each iteration of selection sort.
• Write a JavaScript function that handles duplicate values gracefully in selection sort while preserving stability.

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