Introduction to Sorting

C++

Java

Python

C++

Static Arrays

To sort static arrays, use sort(arr, arr + N) where $N$ is the number of elements to be sorted. The range can also be specified by replacing arr and arr + N with the intended range. For example, sort(arr + 1, arr + 4) sorts indices $[1, 4)$.

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#include <bits/stdc++.h>
using namespace std;

int main() {
	int arr[] = {5, 1, 3, 2, 4};
	int N = 5;
	sort(arr, arr + N);
	for (int i = 0; i < N; i++) cout << arr[i] << " ";  // 1 2 3 4 5
	cout << endl;

	int arr2[] = {5, 1, 3, 2, 4};
	sort(arr2 + 1, arr2 + 4);
	for (int i = 0; i < N; i++) cout << arr2[i] << " ";  // 5 1 2 3 4
}

Java

Static Arrays

To sort a static array, use Arrays.sort(arr).

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import java.util.*;

class Main {
	public static void main(String[] args) {
		int arr[] = {5, 1, 3, 2, 4};
		Arrays.sort(arr);
		for (int i = 0; i < arr.length; i++)
			System.out.print(arr[i] + " ");  // 1 2 3 4 5
	}
}

Python

Static Arrays

To create a static array in Python, the array module is used. Python does not have a built in sort method for arrays, but you can use Python's sorted() function which sorts the array as a list, and returns a list. Then, convert the list back into an array.

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from array import array

# "i" denotes integer type of array elements
arr = array("i", [5, 1, 3, 2, 4])

print(arr)  # Outputs the original array
print(sorted(arr))  # Outputs the sorted array, converted to a list

arr = array("i", sorted(arr))  # Sorting, then converting back into an array
print(arr)

C++

In order to sort a dynamic array, use sort(v.begin(), v.end()) (or sort(begin(v),end(v))). The default sort function sorts the array in ascending order. Similarly, we can specify the range. For example, sort(v.begin() + 1, v.begin() + 4) sorts indices $[1, 4)$.

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#include <bits/stdc++.h>
using namespace std;

int main() {
	vector<int> v{5, 1, 3, 2, 4};
	sort(v.begin(), v.end());
	// Outputs 1 2 3 4 5
	for (int i : v) { cout << i << " "; }
	cout << endl;

Java

In order to sort a dynamic array, use Collections.sort(list). This function sorts the array in ascending order by default.

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import java.util.*;

class Main {
	public static void main(String[] args) {
		List<Integer> arr = new ArrayList<Integer>(Arrays.asList(5, 1, 3, 2, 4));
		Collections.sort(arr);
		System.out.println(arr);  // Outputs [1, 2, 3, 4, 5]
	}
}

Python

There's two main ways to sort a list in Python. You can use sorted(arr), which returns a new list and doesn't modify the old one, or arr.sort(), which sorts the list in place.

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arr = [5, 1, 3, 2, 4]
print(sorted(arr))  # Outputs [1, 2, 3, 4, 5]
print(arr)  # Outputs the original array

arr.sort()
print(arr)  # Outputs [1, 2, 3, 4, 5]

For more on sorting in Python, see this link.

C++

By default, C++ pairs are sorted by first element and then second element in case of a tie.

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#include <bits/stdc++.h>
using namespace std;

int main() {
	vector<pair<int, int>> v{{1, 5}, {2, 3}, {1, 2}};
	sort(v.begin(), v.end());

	/*
	 * Outputs:
	 * 1 2
	 * 1 5
	 * 2 3
	 */
	for (pair<int, int> p : v) { cout << p.first << " " << p.second << endl; }
}

Tuples are sorted similarly.

Java

You'll need to define your own custom comparator. This is covered in Silver.

Python

By default, Python tuples sort by first element, then second element, and so on in case of repeated ties.

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arr = [(1, 5), (2, 3), (1, 2)]
arr = sorted(arr)
print(arr)  # Outputs [(1, 2), (1, 5), (2, 3)]