Selection Sort

Key Points

• ›Makes exactly n−1 swaps regardless of input — useful when writes are expensive
• ›Always O(n²) — does not benefit from pre-sorted data
• ›In-place and simple to implement
• ›Not stable by default (swapping can change relative order of equal elements)
• ›Best suited for small arrays or when minimising swaps matters

Interactive Visualizer

Code Examples

func selectionSort(_ arr: inout [Int]) {
    let n = arr.count
    for i in 0..<n - 1 {
        var minIdx = i
        for j in i + 1..<n {
            if arr[j] < arr[minIdx] { minIdx = j }
        }
        if minIdx != i { arr.swapAt(i, minIdx) }
    }
}

var nums = [64, 25, 12, 22, 11]
selectionSort(&nums)
print(nums)  // [11, 12, 22, 25, 64]

Practice Problems