Three way Partitioning of an Array around a Given Range in C++

October 13, 2022

Three way Partitioning of an Array around a Given Range in C++

 

Here, in this page we will discuss the program for Three way partitioning of an array around a given range in C++ programming language. We are given with an array and a range say [low, high], we need to partition the array in such a way,

  • All the elements less than low value, should come first.
  • Elements between the low and high value come in middle.
  • All elements greater than high should come at the last.
Three way Partitioning of an Array around a Given Range in C++

Method 1 :

  • Take the size of the array from the user and store it in variable say n.
  • Now, declare an array of n size and take n elements of the array from the use.
  • Now, take the lower limit and upper limit of the range from the user and store them in variable say low and high respectively.
  • Now, sort the array after sorting the array got partitioned.

Note : By this algorithm the order of the array can’t be maintained.

Time and Space Complexities :

  • Time-Complexity : O(nlogn)
  • Space-Complexity : O(1)
Partitioning of array

Code for Three way Partitioning of an Array around a given Range in C++

Run 
#include<bits/stdc++.h>
using namespace std;
int main(){

  int n;
  cin>>n;

  int a[n];
  for(int i=0; i<n; i++) cin>>a[i];

  int low, high;
  cin>>low>>high;

  sort(a, a+n);

  for(int i=0; i<n; i++)
  cout<<a[i]<<" ";

}
Input :
10
2 89 34 16 17 10 11 78 30 19
15 20

Output :
2 10 11 16 17 19 30 34 89 78
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Method 2 :

  • Take the size of the array from the user and store it in variable say n.
  • Now, declare an array of n size and take n elements of the array from the use.
  • Now, take the lower limit and upper limit of the range from the user and store them in variable say low and high respectively.
  • Call getPartition function, in that function pass the array, size and low and high value of the range.
  • In the getPartition function,
  • Declare two pointer one is ptr1 set at 0 index and another is ptr2 set at last index i.e, n-1.
  • Now, traverse the array till i<=ptr2.
  • Check if current value is lower than low value than swap it with ptr1 pointing value, and increase the value of ptr1 and i.
  • Else if current value is greater than high than swap it with ptr2 value, and decrease the value of ptr2 .
  • Otherwise increase the value of i.

Time and Space Complexities :

  • Time-Complexity : O(n)
  • Space-Complexity : O(1)

Code for Three way Partitioning of an Array around a given Range in C++

Run 
#include<bits/stdc++.h>
using namespace std;
void getPartition(int a[], int n, int low, int high)
{
   int ptr1 = 0, ptr2 = n-1;
   for (int i=0; i<= ptr2;)
   {
      if (a[i] < low) swap(a[i++], a[ptr1++]); else if (a[i] > high)
      swap(a[i], a[ptr2--]);
      else
      i++;
    }
}

int main(){

  int n;
  cin>>n;

  int a[n];
  for(int i=0; i<n; i++) cin>>a[i];

  int low, high;
  cin>>low>>high;

  getPartition(a, n, low, high);

  for(int i=0; i<n; i++)
  cout<<a[i]<<" ";

}
Input :
10
2 89 34 16 17 10 11 78 30 19
15 20

Output :
2 10 11 16 17 19 30 34 89 78

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