Selection Sort in DSA (PHP) – Complete Guide

📌 What is Selection Sort?

Selection Sort ek simple sorting algorithm hai jisme hum array me se smallest element select karte hain aur usko starting position par rakh dete hain.

👉 Har iteration me ek minimum element choose hota hai aur correct position pe swap hota hai.

⚙️ How Selection Sort Works

Step-by-step:

Array me se smallest element find karo
Usko first position se swap karo
Phir remaining array me se next smallest find karo
Process repeat karo jab tak array sort na ho jaye

📊 Example (Dry Run)

Array:

[64, 25, 12, 22, 11]

[64, 25, 12, 22, 11]

Pass 1:

Minimum = 11
👉 Swap with 64
➡️ [11, 25, 12, 22, 64]

Pass 2:

Minimum = 12
👉 Swap with 25
➡️ [11, 12, 25, 22, 64]

Pass 3:

Minimum = 22
👉 Swap with 25
➡️ [11, 12, 22, 25, 64]

Final Sorted Array:

[11, 12, 22, 25, 64]

[11, 12, 22, 25, 64]

💻 Selection Sort in PHP (Code Example)

<?php
function selectionSort($arr) {
    $n = count($arr);    for ($i = 0; $i < $n - 1; $i++) {
        $minIndex = $i;        for ($j = $i + 1; $j < $n; $j++) {
            if ($arr[$j] < $arr[$minIndex]) {
                $minIndex = $j;
            }
        }        // Swap
        $temp = $arr[$minIndex];
        $arr[$minIndex] = $arr[$i];
        $arr[$i] = $temp;
    }    return $arr;
}// Example
$array = [64, 25, 12, 22, 11];
$sortedArray = selectionSort($array);
print_r($sortedArray);
?>

<?php
function selectionSort($arr) {
    $n = count($arr);    for ($i = 0; $i < $n - 1; $i++) {
        $minIndex = $i;        for ($j = $i + 1; $j < $n; $j++) {
            if ($arr[$j] < $arr[$minIndex]) {
                $minIndex = $j;
            }
        }        // Swap
        $temp = $arr[$minIndex];
        $arr[$minIndex] = $arr[$i];
        $arr[$i] = $temp;
    }    return $arr;
}// Example
$array = [64, 25, 12, 22, 11];
$sortedArray = selectionSort($array);
print_r($sortedArray);
?>

⚡ Key Insight

👉 Selection Sort me minimum element ko select karna main idea hai, isliye naam “Selection Sort”.

⏱️ Time & Space Complexity

Case	Time Complexity
Best Case	O(n²)
Average	O(n²)
Worst Case	O(n²)

Space Complexity:
👉 O(1) (in-place)

👍 Advantages

Simple aur easy samajhne wala
Minimum number of swaps
Memory efficient

👎 Disadvantages

Slow for large data
Always O(n²), even if sorted
Not stable sorting algorithm

🎯 When to Use Selection Sort?

Small datasets
Jab swaps minimize karne ho
Learning DSA basics

🚀 Selection Sort vs Bubble Sort

Feature	Selection Sort	Bubble Sort
Swaps	Less	More
Time Complexity	O(n²)	O(n²)
Stability	Not Stable	Stable
Use Case	Small data	Learning

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