Selection Sort - JavaScript DSA

Repeatedly find the index of the smallest remaining element and swap it into the next "sorted prefix" slot. Unlike bubble sort, only one swap per pass.

Algorithm

Canonical input [5, 1, 4, 2, 8] finishes after four passes, with two real swaps (passes 0 and 1) and two skip-swap passes (minIdx === i). Final array [1, 2, 4, 5, 8].

running minimum `minIdx` tracks the index of the smallest value seen in `arr[i..]`.

sorted prefix After each pass, `arr[0..i]` is the final sorted prefix.

Visual walkthrough

The pinned input [5, 1, 4, 2, 8] sorts with two real swaps. The frames keep the running minimum and swap positions visible.

Step 1 - First scan finds 1

In the first pass, min_idx moves from 5 to 1.

Step 2 - Swap 5 and 1

The smallest value moves into the first sorted slot.

Step 3 - Second scan finds 2

In the unsorted suffix, 2 is smaller than 5 and becomes the next minimum.

Step 4 - Sorted after two swaps

Swapping 5 and 2 gives [1, 2, 4, 5, 8]; later passes find no real swap.

Basic Implementation

                            basic.js
                        

                            const arr = [5, 1, 4, 2, 8];
const n = arr.length;
for (let i = 0; i < n - 1; i++) {
    let minIdx = i;
    for (let j = i + 1; j < n; j++) {
        if (arr[j] < arr[minIdx]) {
            minIdx = j;
        }
    }
    if (minIdx !== i) {
        const tmp = arr[i];
        arr[i] = arr[minIdx];
        arr[minIdx] = tmp;
    }
}
console.log(JSON.stringify(arr));

                        

Complexity

Time: O(n^2) regardless of input order
Space: O(1)
Stable: no
Swap count: at most n-1

Implementation notes

JavaScript: same loop shape as Python/Java. The if (minIdx !== i) guard is the canonical skip-swap variant from the lesson spec.
The replay highlights the current minIdx distinctly from the scanning index j so the viewer sees the running minimum travel.