insertion sort algorithm description with implementation in C++,JAVA and PYTHON

1. Algorithms
Insertion Sort
Abdelrahman M. Saleh

2. List of contents
● Introduction
● Example w/ illustrating figures
● Algorithm
● implementation (Java, C++, Python)
● Performance Runtime
○ Best, Average and worst cases.
● Execution
● Other Notes

3. Introduction
● simple sorting algorithm that works the way we sort playing cards
in our hands.
● used when number of elements is small.
● It can also be useful when input array is almost sorted,
only few elements are misplaced in complete big array.

4. Example w/ illustrating figures
Source : geeksforgeeks.org

5. Algorithm .
Loop from i = 1 to length.
Pick element arr[i]
If (i=1) then skip
Other i => insert it into sorted sequence arr[0...i-1] .

6. Implementation

7. C++ .
void insertionSort(int a[], int len)
{
int i, j, key ;
for(j=1; j<len; j++)
{
key = a[j] ;
i = j-1 ;
while(i>(-1) && a[i] > key)
{
a[i+1] = a[i] ;
i-- ;
}
a[i+1] = key ;
}
}

8. JAVA .
void sort(int a[])
{
int len = a.length;
for (int i=1; i<len; ++i)
{
int key = a[i];
int j = i-1;
while (j>=0 && a[j] > key)
{
a[j+1] = a[j];
j = j-1;
}
a[j+1] = key;
}
}

9. Python .
def insertionSort(a):
for i in range(1, len(a)):
key = a[i]
j = i-1
while j >=0 and key < a[j] :
a[j+1] = a[j]
j -= 1
a[j+1] = key

10. Performance Runtime
● Time complexity Θ(n2
) .
● Best Case : When Array is sorted Θ(n) .
● Worst Case : when array is sorted in reverse order .

11. Execution .
Input array : [9, 11, 8, 7, 6]
First Action : [9, 11, 8, 7, 6]
Move item : 11 .
Move item : 9 .
Sorted item : 8, position => 0 .
Second Action : [8, 9, 11, 7, 6] .
Move item : 11 .
Move item : 9 .
Sorted item : 7, position => 0 .
Third Action : [7, 8, 9, 11, 6]
Move item : 11 .
Move item : 9 .
Move item : 8 .
Move item : 7 .
Sorted item : 6 , position => 0 .
Output array : [6, 7, 8, 9, 11] .

12. Other Notes .
● Algorithmic Paradigm: Incremental Approach
● Sorting In Place: Yes
● Stable: Yes
● Online: Yes