Sort

Last Updated: 2024-01-20

interface Sorter {
    public  <T extends Comparable<? super T>> void sort(T[] a);
}

Quick Sort

class QuickSorter implements Sorter {
    public <T extends Comparable<? super T>> void sort(T[] a) {
        sort(a, 0, a.length - 1);
    }

    public <T extends Comparable<? super T>> void sort(T[] a, int low, int high) {
        T pivot = a[(low+high)/2];
        int i = low, j = high;
        while (i <= j) {
            while (a[i].compareTo(pivot) < 0) i++;
            while (a[j].compareTo(pivot) > 0) j--;
            T tmp = a[j];
            a[j--] = a[i];
            a[i++] = tmp;
        }
        if (low < j)
            sort(a, low, j);
        if (i < high)
            sort(a, i, high);
    }
}

in python

def qsort(L):
    if L == []:
        return []
    pivot = L[0]
    return (qsort([x for x in L[1:] if x < pivot]) +
            [pivot] +
            qsort([x for x in L[1:] if x >= pivot]))

Heap Sort

class HeapSorter implements Sorter {
    public <T extends Comparable<? super T>> void sort(T[] a) {
        sort(a, 0, a.length - 1);
    }

    public <T extends Comparable<? super T>> void sort(T[] a, int low, int high) {
        int size = a.length;

        // Build Heap
        for (int k = size / 2; k >= 0; k--) {
            sink(a, k, size);
        }

        //Sort
        while (size > 1) {
            swap(a, 0, --size);
            sink(a, 0, size);
        }
    }

    private <T extends Comparable<? super T>> void sink(T[] a, int k, int size) {
        int l = 2 * k;
        int r = 2 * k + 1;
        int largest;
        if (l < size && a[l].compareTo(a[k]) > 0)
            largest = l;
        else
            largest = k;
        if (r < size && a[r].compareTo(a[largest]) > 0)
            largest = r;
        if (largest != k) {
            swap(a, k, largest);
            sink(a, largest, size);
        }
    }

    private <T extends Comparable<? super T>> void swap(T[] a, int i, int j) {
        T tmp = a[i];
        a[i] = a[j];
        a[j] = tmp;
    }
}

insertion sort is the algorithm of choice either when the data is nearly sorted (because it is adaptive) or when the problem size is small (because it has low overhead).

C++

vector<int> vals = {-1, -2, -3, 1, 2, 3, 0};
int p = 2;

sort(vals.begin(),
     vals.end(),
     [p](int a, int b) {
        return pow(a, p) < pow(b, p);
        });

Java 8+

list.stream().sorted()

Or

list.sort((Foo o1, Foo o2) -> o1.getBar() - o2.getBar());

Reverse

list.stream().sorted(Comparator.reverseOrder())

Use Collections.sort()

Collections.sort(vals, (a, b) ->
        Integer.compare(Math.pow(a, p), Math.pow(b, p)));

JavaScript

Sort array

arr.sort((a,b) => { return parseFloat(a.data) - parseFloat(b.data) } );

arr.sort((a,b) => { return a.str.localeCompare(b.str) } );

arr.sort((a,b) => { return a.str.toUpperCase().localeCompare(b.str.toUpperCase() } );

Sort object

const sortedObj = Object.keys(obj)
  .sort()
  .reverse()
  .reduce((newObj, k) => {
    newObj[k] = obj[k];
    return newObj;
  }, {});

Python

By default, sort, sorted, heapq can sort tuples: the first element first and on the second element second. Can specify key to override default. cmp is deprecated in Python 3

sorted_data = sorted(data, key=lambda x: x['key'])

or sorts in place

data.sort(key=lambda x: x['key'])

Sort on multiple keys, suppose x is a tuple (int, int, boolean)

data.sort(key=lambda x: (x[0], not x[2]))

Sort dict

import operator
sorted_x = sorted(x.iteritems(), key=operator.itemgetter(1), reverse=True)

https://docs.python.org/3/howto/sorting.html

Rust

let mut vals = [-1, -2, -3, 1, 2, 3, 0];
let p = 2;

vals.sort_by(|a :&isize, b :&isize|
                a.pow(p).cmp(&b.pow(p)));