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c++ quicksort Code Example
quick sort c++ 
#include <iostream>
using namespace std;
// Swap two elements - Utility function  
void swap(int* a, int* b) 
{ 
    int t = *a; 
    *a = *b; 
    *b = t; 
} 
   
// partition the array using last element as pivot
int partition (int arr[], int low, int high) 
{ 
    int pivot = arr[high];    // pivot 
    int i = (low - 1);   
   
    for (int j = low; j <= high- 1; j++) 
    { 
        //if current element is smaller than pivot, increment the low element
        //swap elements at i and j
        if (arr[j] <= pivot) 
        { 
            i++;    // increment index of smaller element 
            swap(&arr[i], &arr[j]); 
        } 
    } 
    swap(&arr[i + 1], &arr[high]); 
    return (i + 1); 
} 
   
//quicksort algorithm
void quickSort(int arr[], int low, int high) 
{ 
    if (low < high) 
    { 
        //partition the array 
        int pivot = partition(arr, low, high); 
   
        //sort the sub arrays independently 
        quickSort(arr, low, pivot - 1); 
        quickSort(arr, pivot + 1, high); 
    } 
} 
   
void displayArray(int arr[], int size) 
{ 
    int i; 
    for (i=0; i < size; i++) 
        cout<<arr[i]<<"\t"; 
      
} 
   
int main() 
{ 
    int arr[] = {12,23,3,43,51,35,19,45}; 
    int n = sizeof(arr)/sizeof(arr[0]); 
    cout<<"Input array"<<endl;
    displayArray(arr,n);
    cout<<endl;
    quickSort(arr, 0, n-1); 
    cout<<"Array sorted with quick sort"<<endl; 
    displayArray(arr,n); 
    return 0; 
}
quick sort c++ 
// C++ Implementation of the Quick Sort Algorithm.
#include <iostream>
using namespace std;
 
int partition(int arr[], int start, int end)
{
 
    int pivot = arr[start];
 
    int count = 0;
    for (int i = start + 1; i <= end; i++) {
        if (arr[i] <= pivot)
            count++;
    }
 
    // Giving pivot element its correct position
    int pivotIndex = start + count;
    swap(arr[pivotIndex], arr[start]);
 
    // Sorting left and right parts of the pivot element
    int i = start, j = end;
 
    while (i < pivotIndex && j > pivotIndex) {
 
        while (arr[i] <= pivot) {
            i++;
        }
 
        while (arr[j] > pivot) {
            j--;
        }
 
        if (i < pivotIndex && j > pivotIndex) {
            swap(arr[i++], arr[j--]);
        }
    }
 
    return pivotIndex;
}
 
void quickSort(int arr[], int start, int end)
{
 
    // base case
    if (start >= end)
        return;
 
    // partitioning the array
    int p = partition(arr, start, end);
 
    // Sorting the left part
    quickSort(arr, start, p - 1);
 
    // Sorting the right part
    quickSort(arr, p + 1, end);
}
 
int main()
{
 
    int arr[] = { 9, 3, 4, 2, 1, 8 };
    int n = 6;
 
    quickSort(arr, 0, n - 1);
 
    for (int i = 0; i < n; i++) {
        cout << arr[i] << " ";
    }
 
    return 0;
}
Source: www.geeksforgeeks.org
c++ code for quicksort 
#include<bits/stdc++.h>
using namespace std;
int partition(int a[],int low,int high)
{
    int pivot =a[high],i=low-1,j=low;
    for(j=low;j<=high-1;j++)
    {
        if(a[high]>=a[j])
        {
            i++;
            swap(a[i],a[j]);
        }
    }
    swap(a[i+1],a[high]);
    return i+1;
    
}
void quicksort(int a[],int low,int high)
{
    if(low<high)
    {
        int  t = partition(a,low,high);
        quicksort(a,low,t-1);
        quicksort(a,t+1,high);
    }
}
int main()
{
    //quick sort
    int a[8] = {3,10,8,51,92,6,2,1};
    quicksort(a,0,7);
    for(int i=0;i<8;i++)
    {
        cout<<a[i]<<" ";
    }
    
    return 0;
}
quick sort c++ 
#include<iostream>
using namespace std;

int solve(int arr[], int s, int e, int &pivotIndex)
{
    int i=s,j=e;
    while(i<pivotIndex && j>pivotIndex)
    {
        while(arr[i]<=arr[pivotIndex])
        {
            i++;
        }
        while(arr[j]>arr[pivotIndex])
        {
            j--;
        }
        
        if(i<pivotIndex && j>pivotIndex)
        {
            swap(arr[i++],arr[j--]);
        }
    }
    
}

int partition(int arr[], int s, int e)
{
    int count=0;
    int pivot = arr[s];
    for(int i=s+1;i<=e;i++)
    {
        if(arr[i]<=pivot)
        {
            count++;
        }
    }

    int pivotIndex = s + count;
    swap(arr[pivotIndex], arr[s]);

    return solve(arr,s,e,pivotIndex);

    /* Or we can do same here no need to call function
    int i=s,j=e;
    while(i<pivotIndex && j>pivotIndex)
    {
        while(arr[i]<=arr[pivotIndex])
        {
            i++;
        }
        while(arr[j]>arr[pivotIndex])
        {
            j--;
        }
        
        if(i<pivotIndex && j>pivotIndex)
        {
            swap(arr[i++],arr[j--]);
        }
    }

    return pivotIndex;
    
    */
}

void helper(int arr[], int s, int e)
{
    if(s>=e)
    {
        return;
    }

    // partition of array
    int p = partition(arr,s,e);

    // sorting left part
    helper(arr,s,p-1);

    // sorting right part
    helper(arr,p+1,e);

}

void quickSort(int input[], int size) {

    helper(input,0,size-1);
}

int main()
{
    int size = 6;
    int input[1000] = {5,6,0,9,1,4};
    
    quickSort(input,size);
    for(int i=0;i<size;i++)
    {
        cout<<input[i]<<" ";
    }

}
quick sort c++ 
/* C++ implementation of QuickSort */
#include <bits/stdc++.h>
using namespace std;
 
// A utility function to swap two elements
void swap(int* a, int* b)
{
    int t = *a;
    *a = *b;
    *b = t;
}
 
/* 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]; // pivot
    int i = (low - 1); // Index of smaller element and indicates the right position of pivot found so far
 
    for (int j = low; j <= high - 1; j++)
    {
        // If current element is smaller than the pivot
        if (arr[j] < pivot)
        {
            i++; // increment index of smaller element
            swap(&arr[i], &arr[j]);
        }
    }
    swap(&arr[i + 1], &arr[high]);
    return (i + 1);
}
 
/* The main function that implements QuickSort
arr[] --> Array to be sorted,
low --> Starting index,
high --> Ending index */
void quickSort(int arr[], int low, int high)
{
    if (low < high)
    {
        /* pi is partitioning index, arr[p] is now
        at right place */
        int pi = partition(arr, low, high);
 
        // Separately sort elements before
        // partition and after partition
        quickSort(arr, low, pi - 1);
        quickSort(arr, pi + 1, high);
    }
}
 
/* Function to print an array */
void printArray(int arr[], int size)
{
    int i;
    for (i = 0; i < size; i++)
        cout << arr[i] << " ";
    cout << endl;
}
 
// Driver Code
int main()
{
    int arr[] = {10, 7, 8, 9, 1, 5};
    int n = sizeof(arr) / sizeof(arr[0]);
    quickSort(arr, 0, n - 1);
    cout << "Sorted array: \n";
    printArray(arr, n);
    return 0;
}
 
// This code is contributed by rathbhupendra
Source: www.geeksforgeeks.org
c++ quicksort 
/* low  --> Starting index,  high  --> Ending index */
quickSort(arr[], low, high)
{
    if (low < high)
    {
        /* pi is partitioning index, arr[p] is now
           at right place */
        pi = partition(arr, low, high);

        quickSort(arr, low, pi - 1);  // Before pi
        quickSort(arr, pi + 1, high); // After pi
    }
}
Source: www.geeksforgeeks.org



Cpp

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Category:
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Sub Category:
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