Must Know Sorting Algorithms

✅ 1. Selection Sort

public class SelectionSort {
    public static void selectionSort(int[] arr) {
        int n = arr.length;
        for (int i = 0; i < n - 1; i++) {
            int minIdx = i;
            for (int j = i + 1; j < n; j++) {
                if (arr[j] < arr[minIdx])
                    minIdx = j;
            }
            int temp = arr[minIdx];
            arr[minIdx] = arr[i];
            arr[i] = temp;
        }
    }
}

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✅ 2. Bubble Sort

public class BubbleSort {
    public static void bubbleSort(int[] arr) {
        int n = arr.length;
        boolean swapped;
        for (int i = 0; i < n - 1; i++) {
            swapped = false;
            for (int j = 0; j < n - 1 - i; j++) {
                if (arr[j] > arr[j + 1]) {
                    int temp = arr[j];
                    arr[j] = arr[j + 1];
                    arr[j + 1] = temp;
                    swapped = true;
                }
            }
            if (!swapped) break; // Optimized
        }
    }
}

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✅ 3. Insertion Sort

public class InsertionSort {
    public static void insertionSort(int[] arr) {
        for (int i = 1; i < arr.length; i++) {
            int key = arr[i], j = i - 1;
            while (j >= 0 && arr[j] > key)
                arr[j + 1] = arr[j--];
            arr[j + 1] = key;
        }
    }
}

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✅ 4. Merge Sort

 // Merge Sort function
    public static void mergeSort(int[] arr, int left, int right) {
        if (left < right) {
            // Find the middle point
            int mid = left + (right - left) / 2;

            // Sort first and second halves
            mergeSort(arr, left, mid);
            mergeSort(arr, mid + 1, right);

            // Merge the sorted halves
            merge(arr, left, mid, right);
        }
    }

    // Merge two subarrays of arr[]
    public static void merge(int[] arr, int left, int mid, int right) {
        // Sizes of two subarrays
        int n1 = mid - left + 1;
        int n2 = right - mid;

        // Create temp arrays
        int[] L = new int[n1];
        int[] R = new int[n2];

        // Copy data to temp arrays
        for (int i = 0; i < n1; ++i)
            L[i] = arr[left + i];
        for (int j = 0; j < n2; ++j)
            R[j] = arr[mid + 1 + j];

        // Merge the temp arrays

        int i = 0, j = 0;
        int k = left;

        while (i < n1 && j < n2) {
            if (L[i] <= R[j]) {
                arr[k++] = L[i++];
            } else {
                arr[k++] = R[j++];
            }
        }

        // Copy remaining elements of L[]
        while (i < n1) {
            arr[k++] = L[i++];
        }

        // Copy remaining elements of R[]
        while (j < n2) {
            arr[k++] = R[j++];
        }
    }

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✅ 5. Heap Sort

public class HeapSort {
    public static void heapSort(int[] arr) {
        int n = arr.length;

        // Build max heap
        for (int i = n / 2 - 1; i >= 0; i--)
            heapify(arr, n, i);

        // Extract elements one by one
        for (int i = n - 1; i > 0; i--) {
            int temp = arr[0]; arr[0] = arr[i]; arr[i] = temp;
            heapify(arr, i, 0);
        }
    }

    private static void heapify(int[] arr, int n, int i) {
        int largest = i, l = 2 * i + 1, r = 2 * i + 2;

        if (l < n && arr[l] > arr[largest]) largest = l;
        if (r < n && arr[r] > arr[largest]) largest = r;

        if (largest != i) {
            int temp = arr[i]; arr[i] = arr[largest]; arr[largest] = temp;
            heapify(arr, n, largest);
        }
    }
}

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✅ 6. Quick Sort

public class QuickSort {
    public static void quickSort(int[] arr, int low, int high) {
        if (low < high) {
            int pi = partition(arr, low, high);

            quickSort(arr, low, pi - 1);
            quickSort(arr, pi + 1, high);
        }
    }

    private static int partition(int[] arr, int low, int high) {
        int pivot = arr[high], i = low - 1;
        for (int j = low; j < high; j++) {
            if (arr[j] <= pivot) {
                i++;
                int temp = arr[i]; arr[i] = arr[j]; arr[j] = temp;
            }
        }
        int temp = arr[i + 1]; arr[i + 1] = arr[high]; arr[high] = temp;
        return i + 1;
    }
}