How to Sort an Array in Descending Order using STL in C++?

Sort an array in descending order means arranging the elements in such a way that the largest element at first place, second largest at second place and so on. In this article, we will learn how to sort an array in descending order using STL in C++.

Examples

Input: arr[] = {11, 9, 45, 21};
Output: 78 45 23 21 11 9
Explanation: As the elements are sorted in decreasing order.

Input: arr[] = {11, 9, 56, 1, 89, 7};
Output: 89 56 11 9 7 1
Explanation: As the elements are sorted in decreasing order.

C++ STL provides the following different methods to sort an array in descending order:

Using std::sort() Function

C++ STL provides the std::sort() algorithm to sort the given range of elements. We can also sort the array using this function. By default, it sorts the array in ascending order, but we can change it to descending order using custom comparator function.

Syntax

std::sort(first, last, comp);

where, first and last are the iterator to the beginning and the end of the range, and comp is the custom comparator.

Example

// C++ Program to sort an array in descending
// order using std::sort()
#include <bits/stdc++.h>
using namespace std;

// Comparator function
bool comp (int a, int b) {
  return a > b;
}

int main() {
    int arr[] = {11, 9, 45, 21};
    int n = sizeof(arr) / sizeof(arr[0]);

    // sort an array in descending order along
    // with custom comparator
    sort(arr, arr + n, comp);

    for (auto i : arr)
        cout << i << " ";
    return 0;
}

45 21 11 9 

Time Complexity: O(n * log n), where n is the size of the array.
Auxiliary Space: O(1)

Note: We also can use the std::greater<>() functor as comparator in this code.

Using std::stable_sort() Function

We can also use std::stable_sort() function is similar to the std::sort() function but preserve the relative order of equal elements in the array while sorting. It also sorts the array in the ascending order by default, so we have to provide custom comparator

Syntax

std::stable_sort(first, last, comp);

where, first and last are the iterator to the beginning and the end of the range, and comp is the custom comparator.

Example

// C++ Program to sort an array in descending
// order using std::stable_sort()
#include <bits/stdc++.h>
using namespace std;

int main() {
    int arr[] = {11, 9, 45, 21};
    int n = sizeof(arr) / sizeof(arr[0]);

    // sort an array in descending order
    stable_sort(arr, arr + n, greater<>());

    for (auto i : arr)
        cout << i << " ";
    return 0;
}

45 21 11 9 

Time Complexity: O(n * log n), where n is the size of the array.
Auxiliary Space: O(1)

Using std::partial_sort() Function

We can sort an array in descending order using std::partial_sort() function provided by STL in C++. This function is generally used to sort a part of the given range, but we can modify it to sort the whole range. We also have to provide custom comparator for sorting in decreasing order.

Syntax

std::partial_sort(first, middle, last, comp);

where, first and last are the iterator to the beginning and the end of the range, and comp is the custom comparator. middle is the iterator to the point till which we have to sort starting from first.

Example

// C++ Program to sort an array in descending
// order using std::partial_sort()
#include <bits/stdc++.h>
using namespace std;

int main() {
    int arr[] = {11, 9, 45, 21};
    int n = sizeof(arr) / sizeof(arr[0]);

    // Sort array in descending order
    partial_sort(arr, arr + n, arr + n,
                 greater<int>());

    for (auto i: arr)
        cout << i << " ";
    return 0;
}

45 21 11 9 

Time Complexity: O(n * log n), where n is the size of the array.
Auxiliary Space: O(1)