partition_copy in C++ STL
Last Updated :
27 Nov, 2022
partition_copy is the inbuilt function defined in <algorithm> library in STL. partition_copy function duplicates the partitioned elements into the various containers given in its parameters. It requires 5 arguments which are the beginning and ending position of the container, the beginning position of a new container where elements have to be copied (elements returning true for condition), the beginning position of a new container where other elements have to be copied (elements returning false for condition) and the condition. For this function, new containers must be resized.
Syntax:
partition_copy(iterator it1_first, iterator it1_end, iterator it2_first, iterator it3_first, cond)
Parameters:
iterator it1_first: Iterator pointing to the start of initial container from which we want to do the partition.
iterator it1_end: Iterator pointing to the end of initial container from which we want to do the partition.
iterator it2_first: Iterator pointing to the start of new container where other elements have to be copied based on the conditions specified.
iterator it3_first: Iterator pointing to the start of another new container where other elements have to be copied based on the conditions specified.
cond: A user defined function which help to partition the element into new containers based on the condition in this function.
Time and Space Complexity:
Time Complexity: O(n)
Auxiliary Space: O(n)
where n is the number of elements in the initial vector.
Example 1: Using the partition_copy() function to divide the given vector into two parts based on the condition that the number is even or odd in the vector.
Code:
C++
// C++ code to demonstrate the working of
// partition_copy()
#include<iostream>
#include<algorithm>
#include<vector>
using namespace std;
int main()
{
// Initializing the vector
vector<int> arr = { 1, 2, 3, 4, 5, 6 };
// Declaring vectors for storing
// partitioned elements
vector<int> arr1,arr2;
// Resizing vectors to suitable size using
// count_if() and resize()
int n = count_if (arr.begin(), arr.end(), [](int x)
{
return x%2==0;
} );
arr1.resize(n);
arr2.resize(arr.size()-n);
// Using partition_copy() to copy partitions
partition_copy(arr.begin(), arr.end(), arr1.begin(),
arr2.begin(), [](int x)
{
return x%2==0;
});
// Displaying partitioned vectors
cout << "The elements that return true for given condition ";
for (int &x : arr1)
cout << x << " ";
cout << endl;
cout << "The elements that return false for given condition ";
for (int &x : arr2)
cout << x << " ";
cout << endl;
return 0;
}
OutputThe elements that return true for given condition 2 4 6
The elements that return false for given condition 1 3 5
Example 2: Using the partition_copy() function to divide the given vector into two parts based on the condition that the number is a power of two or not.
Code:
C++
// C++ code to demonstrate the working of
// partition_copy()
#include<bits/stdc++.h>
using namespace std;
int main()
{
// Initializing the vector
vector<int> arr = { 1, 2, 3, 4, 5, 6 };
// Declaring vectors for storing
// partitioned elements
vector<int> arr1,arr2;
// Resizing vectors to suitable size using
// count_if() and resize()
int n = count_if (arr.begin(), arr.end(), [](int x)
{
if (x == 0)
return false;
return (ceil(log2(x)) == floor(log2(x)));
} );
arr1.resize(n);
arr2.resize(arr.size()-n);
// Using partition_copy() to copy partitions
partition_copy(arr.begin(), arr.end(), arr1.begin(),
arr2.begin(), [](int x)
{
// code to check if number is power of two or not
if (x == 0)
return false;
return (ceil(log2(x)) == floor(log2(x)));
});
// Displaying partitioned vectors
cout << "The elements that return true for given condition ";
for (int &x : arr1)
cout << x << " ";
cout << endl;
cout << "The elements that return false for given condition ";
for (int &x : arr2)
cout << x << " ";
cout << endl;
return 0;
}
OutputThe elements that return true for given condition 1 2 4
The elements that return false for given condition 3 5 6
