Lecture 22: Sorting2 -- Insertion

Objectives of this lecture

q Lean the Insertion Sorting Method.

Insertion Sort:

q This is another quadratic sorting method.

q It has advantage over selection sort when the list is already sorted – it doest it in linear order (n times).

q On a random data however, they are about the same.

q In this method, the list is conceptually divided into a destination sub-list a₀, … a_i-1 and a source sub-list, a_i … a_n-1.

q In each iteration, the ith element of the source sub-list is picked and inserted at its proper position in the destination sub-list.

void InsertionSort(int list[])

{ int i, j , temp;

for(i = 1; i < MAX_SIZE ; i++)

{ temp = list[i];

j = i;

while((j-1 >= 0) && list[j-1] > temp)

{ list[j] = list[j-1];

j--;

}

list[j] = temp;

}

}

q The following table shows a trace of insertion sort:

Index	Original	Round1	Round3	Round 3
0	7	2	1	1
1	2	7	2	2
2	1	1	7	4
3	4	4	4	7