We have discussed qsort() in C. C++ STL provides a similar function sort that sorts a vector or array (items with random access)
It generally takes two parameters, the first one being the point of the array/vector from where the sorting needs to begin and the second parameter being the length up to which we want the array/vector to get sorted. The third parameter is optional and can be used in cases such as if we want to sort the elements lexicographically.
By default, the sort() function sorts the elements in ascending order.
Below is a simple program to show the working of sort().
Tóm Tắt
CPP
#include <bits/stdc++.h>
using namespace std;
int main()
{
int arr[] = { 1, 5, 8, 9, 6, 7, 3, 4, 2, 0 };
int n = sizeof(arr) / sizeof(arr[0]);
sort(arr, arr + n);
cout << "\nArray after sorting using "
"default sort is : \n";
for (int i = 0; i < n; ++i)
cout << arr[i] << " ";
return 0;
}
Output
Array after sorting using default sort is : 0 1 2 3 4 5 6 7 8 9
How to sort in descending order?
sort() takes a third parameter that is used to specify the order in which elements are to be sorted. We can pass the “greater()” function to sort in descending order. This function does a comparison in a way that puts greater elements before.
CPP
#include <bits/stdc++.h>
using namespace std;
int main()
{
int arr[] = { 1, 5, 8, 9, 6, 7, 3, 4, 2, 0 };
int n = sizeof(arr) / sizeof(arr[0]);
sort(arr, arr + n, greater<int>());
cout << "Array after sorting : \n";
for (int i = 0; i < n; ++i)
cout << arr[i] << " ";
return 0;
}
Output
Array after sorting : 9 8 7 6 5 4 3 2 1 0
Sort the array only in the given range: To deal with such types of problems we just have to mention the range inside the sort function.
Below is the implementation of above case:
C++
#include <bits/stdc++.h>
using namespace std;
int main()
{
int arr[] = { 0, 1, 5, 8, 9, 6, 7, 3, 4, 2 };
int n = sizeof(arr) / sizeof(arr[0]);
sort(arr + 2, arr + n);
cout << "Array after sorting : \n";
for (int i = 0; i < n; ++i)
cout << arr[i] << " ";
return 0;
}
Output
Array after sorting : 0 1 2 3 4 5 6 7 8 9
How to sort in a particular order?
We can also write our own comparator function and pass it as a third parameter. This “comparator” function returns a value; convertible to bool, which basically tells us whether the passed “first” argument should be placed before the passed “second” argument or not.
For eg: In the code below, suppose intervals {6,8} and {1,9} are passed as arguments in the “compareInterval” function(comparator function). Now as i1.first (=6) < i2.first (=1), so our function returns “false”, which tells us that “first” argument should not be placed before “second” argument and so sorting will be done in order like {1,9} first and then {6,8} as next.
CPP
#include <bits/stdc++.h>
using namespace std;
struct Interval {
int start, end;
};
bool compareInterval(Interval i1, Interval i2)
{
return (i1.start < i2.start);
}
int main()
{
Interval arr[]
= { { 6, 8 }, { 1, 9 }, { 2, 4 }, { 4, 7 } };
int n = sizeof(arr) / sizeof(arr[0]);
sort(arr, arr + n, compareInterval);
cout << "Intervals sorted by start time : \n";
for (int i = 0; i < n; i++)
cout << "[" << arr[i].start << "," << arr[i].end
<< "] ";
return 0;
}
Output
Intervals sorted by start time : [1,9] [2,4] [4,7] [6,8]
The time complexity of std::sort() is:
- Best Case – O(N log N)
- Average Case – O(N log N)
- Worst-Case – O(N log N)
Space Complexity: It may use O( log N) auxiliary space.
C++
#include <algorithm>
#include <iostream>
using namespace std;
template <class T>
class Comparator {
public:
bool operator()(T x1, T x2)
{
return x1 < x2;
}
};
template <class T> bool funComparator(T x1, T x2)
{
return x1 <= x2;
}
void show(int a[], int array_size)
{
for (int i = 0; i < array_size; i++) {
cout << a[i] << " ";
}
}
int main()
{
int a[] = { 1, 5, 8, 9, 6, 7, 3, 4, 2, 0 };
int asize = sizeof(a) / sizeof(int);
cout << "The array before sorting is : ";
show(a, asize);
cout << endl << "The array after sorting is(asc) :";
sort(a, a + asize);
show(a, asize);
cout << endl << "The array after sorting is(desc) :";
sort(a, a + asize, greater<int>());
show(a, asize);
cout << endl
<< "The array after sorting is(asc but our "
"comparator class) :";
sort(a, a + asize, Comparator<int>());
show(a, asize);
cout << endl
<< "The array after sorting is(asc but our "
"comparator function) :";
sort(a, a + asize, funComparator<int>);
show(a, asize);
return 0;
}
Output
The array before sorting is : 1 5 8 9 6 7 3 4 2 0 The array after sorting is(asc) :0 1 2 3 4 5 6 7 8 9 The array after sorting is(desc) :9 8 7 6 5 4 3 2 1 0 The array after sorting is(asc but our comparator class) :0 1 2 3 4 5 6 7 8 9 The array after sorting is(asc but our comparator function) :0 1 2 3 4 5 6 7 8 9
This article is contributed by Shubham Agrawal. Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above
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