Quicksort 1 - Partition


Problem Statement :


The previous challenges covered Insertion Sort, which is a simple and intuitive sorting algorithm with a running time of . In these next few challenges, we're covering a divide-and-conquer algorithm called Quicksort (also known as Partition Sort). This challenge is a modified version of the algorithm that only addresses partitioning. It is implemented as follows:

Step 1: Divide
Choose some pivot element, , and partition your unsorted array, , into three smaller arrays: , , and , where each element in , each element in , and each element in .

Example

In this challenge, the pivot will always be at , so the pivot is .

 is divided into , , and .
Putting them all together, you get . There is a flexible checker that allows the elements of  and  to be in any order. For example,  is valid as well.

Given  and , partition  into , , and  using the Divide instructions above. Return a 1-dimensional array containing each element in  first, followed by each element in , followed by each element in .

Function Description

Complete the quickSort function in the editor below.

quickSort has the following parameter(s):

int arr[n]:  is the pivot element
Returns

int[n]: an array of integers as described above
Input Format

The first line contains , the size of .
The second line contains  space-separated integers  (the unsorted array). The first integer, , is the pivot element, .c


Solution :



title-img 


                            Solution in C :

In   C++  :








#include <map>
#include <set>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <bitset>
#include <cstdio>
#include <vector>
#include <cstdlib>
#include <numeric>
#include <sstream>
#include <iostream>
#include <algorithm>
using namespace std;

/* Head ends here */

void partition(vector <int>  ar) 
{
    vector<int> glist,llist;
    long long i=1, p = ar[0];
    while(i<ar.size())
    {
        if(ar[i]>p)
            glist.push_back(ar[i]);
        else
            llist.push_back(ar[i]);
        i++;
    }
    i=0;
    while(i<llist.size())
    {
        ar[i] = llist[i];
        cout<<llist[i]<<" ";
        i++;
    }
    ar[i]=p;
    cout<<p<<" ";
    i=0;
    while(i<glist.size())
    {
        ar[i+p] = glist[i];
        if(i==glist.size()-1)
            cout<<glist[i]<<endl;
        else
            cout<<glist[i]<<" ";
        i++;
    }
}

/* Tail starts here */

int main() {
   vector <int>  _ar;
   int _ar_size;
cin >> _ar_size;
for(int _ar_i=0; _ar_i<_ar_size; _ar_i++) {
   int _ar_tmp;
   cin >> _ar_tmp;
   _ar.push_back(_ar_tmp); 
}

partition(_ar);
   
   return 0;
}









In   Java  :










/* Head ends here */
import java.util.*;
public class Solution {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
           int n = in.nextInt();
           int[] ar = new int[n];
           for(int i=0;i<n;i++){
              ar[i]=in.nextInt(); 
           }
           partition(ar);
           printArray(ar);
    }
    static void printArray(int[] ar) {
         for(int n: ar){
            System.out.print(n+" ");
         }
           System.out.println("");
    }
    static void partition(int[] ar) {
        int p=ar[0];
        int[] copy=Arrays.copyOf(ar, ar.length);
        int c=0;
        for(int i=1;i<ar.length;i++){
            if(copy[i]<=p){
                ar[c]=copy[i];
                c++;
            }
        }
        ar[c]=p;
        c++;
        for(int j=0;j<ar.length;j++){
            if(copy[j]>p){
                ar[c]=copy[j];
                c++;
            }
        }
    }   
}










In   C  :








#include <stdio.h>
#include <string.h>
#include <math.h>
#include <stdlib.h>
#include <assert.h>

/* Head ends here */
void partition(int ar_size, int *  ar) {

int f,temp=ar[0],j=0,k=0,i;
    int ar1[ar_size],ar2[ar_size];
    for(i=0;i<ar_size;i++)
    {
        if(ar[i]<temp)
        {
            ar1[j]=ar[i];
            j++;
        }
        if(ar[i]>temp)
        {
            ar2[k]=ar[i];
            k++;
           //printf("k=%d\n",k);
        }
       
    }
  /*  ar1[j]=temp;
    j++;
        for(i=0;i<k;i++)
        {
         ar1[j]=ar2[i];
            j++;
        }*/
   // printf("j=%d\n",j);
    for(i=0;i<j;i++)
    printf("%d ",ar1[i]);
    printf("%d ",temp);
    for(i=0;i<k;i++)
        printf("%d ",ar2[i]);
    
}

/* Tail starts here */
int main() {
   
   int _ar_size;
scanf("%d", &_ar_size);
int _ar[_ar_size], _ar_i;
for(_ar_i = 0; _ar_i < _ar_size; _ar_i++) { 
   scanf("%d", &_ar[_ar_i]); 
}

partition(_ar_size, _ar);
   
   return 0;
}










In    Python3 :







size = int(input())
array = input().split(" ")
arr = ['None'] * size
for i in range(size):
    arr[i] = int(array[i])
p = arr[0]
less = [ ]
more = [ ]
for i in range(size):
    if arr[i] < p:
        less.append(arr[i])
    else:
        more.append(arr[i])
for j in range(len(less)):
    print(less[j], end = " ")
for k in range(len(more)):
    print(more[k], end = " ")








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