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java/sorting/QuickSort.java at master · AllAlgorithms/java · GitHub

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// Java program for implementation of QuickSort

class QuickSort

{

/* This function takes last element as pivot,

places the pivot element at its correct

position in sorted array, and places all

smaller (smaller than pivot) to left of

pivot and all greater elements to right

of pivot */

int partition(int arr[], int low, int high)

{

int pivot = arr[high];

int i = (low-1); // index of smaller element

for (int j=low; j<high; j++)

{

// If current element is smaller than or

// equal to pivot

if (arr[j] <= pivot)

{

i++;

// swap arr[i] and arr[j]

int temp = arr[i];

arr[i] = arr[j];

arr[j] = temp;

}

}

// swap arr[i+1] and arr[high] (or pivot)

int temp = arr[i+1];

arr[i+1] = arr[high];

arr[high] = temp;

return i+1;

}

/* The main function that implements QuickSort()

arr[] --> Array to be sorted,

low --> Starting index,

high --> Ending index */

void sort(int arr[], int low, int high)

{

if (low < high)

{

/* pi is partitioning index, arr[pi] is

now at right place */

int pi = partition(arr, low, high);

// Recursively sort elements before

// partition and after partition

sort(arr, low, pi-1);

sort(arr, pi+1, high);

}

}

/* A utility function to print array of size n */

static void printArray(int arr[])

{

int n = arr.length;

for (int i=0; i<n; ++i)

System.out.print(arr[i]+" ");

System.out.println();

}

// Driver program

public static void main(String args[])

{

int arr[] = {10, 7, 8, 9, 1, 5};

int n = arr.length;

QuickSort ob = new QuickSort();

ob.sort(arr, 0, n-1);

System.out.println("sorted array");

printArray(arr);

}

}

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