Sorting algorithms/Insertion sort

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Revision as of 20:28, 11 December 2007 by Epsilon (talk | contribs) (Added CL version)
Task
Sorting algorithms/Insertion sort
You are encouraged to solve this task according to the task description, using any language you may know.

An O(n^2) sorting algorithm which moves elements one at a time into the correct position. The algorithm is as follows (from the wikipedia):

insertionSort(array A)
        for i = 1 to length[A]-1 do
               value = A[i] 
               j = i-1
               while j >= 0 and A[j] > value do 
                        A[j + 1] = A[j]
                        j = j-1
               A[j+1] = value

Writing the algorithm for integers will suffice.

Common Lisp

(defun span (predicate list)
  (let ((tail (member-if-not predicate list)))
    (values (ldiff list tail) tail)))

(defun less-than (x)
  (lambda (y) (< y x)))

(defun insert (list elt)
  (multiple-value-bind (left right) (span (less-than elt) list)
    (append left (list elt) right)))

(defun insertion-sort (list)
  (reduce #'insert list :initial-value nil))


Haskell

insert x [] = [x]
insert x (y:ys) | x <= y    = x:y:ys
insert x (y:ys) | otherwise = y:(insert x ys)

insertionSort :: Ord a => [a] -> [a]
insertionSort = foldr insert []

-- Example use:
-- *Main> insertionSort [6,8,5,9,3,2,1,4,7]
-- [1,2,3,4,5,6,7,8,9]

Java

public static void insertSort(int[] A){
	for(int i = 1; i < A.length; i++){
		int value = A[i];
		int j = i - 1;
		while(j >= 0 && A[j] > value){
			A[j + 1] = A[j];
			j = j - 1;
		}
		A[j + 1] = value;
	}
}

Python

def insertion_sort(l):
    for i in xrange(1, len(l)):
        j = i-1 
        key = l[i]
        while (l[j] > key) and (j >= 0):
           l[j+1] = l[j]
           j -= 1
        l[j+1] = key