Matakuliah
Tahun
Versi
: T0016/Algoritma dan Pemrograman
: 2005
: versi 2
Pertemuan 20
Teknik Sort II
1
Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa
akan mampu :
• Menjelaskan teknik quick sort dan merge
sort
2
Outline Materi
• Pengenalan quick sort
• Pengenalan merge sort
3
Quick Sort
• The quick sort is an in-place, divide-andconquer, massively recursive sort. As a
normal person would say, it's essentially a
faster in-place version of the merge sort.
• The efficiency of the algorithm is majorly
impacted by which element is choosen as
the pivot point. The worst-case efficiency
of the quick sort, O(n2), occurs when the
list is sorted and the left-most element is
chosen.
4
Quick Sort
void quickSort(int numbers[], int array_size) {
q_sort(numbers, 0, array_size - 1);
} void q_sort(int numbers[], int left, int right) {
int pivot, l_hold, r_hold;
l_hold = left;
r_hold = right;
pivot = numbers[left];
while (left < right) {
while ((numbers[right] >= pivot) && (left < right))
right--;
5
Quick Sort
if (left != right) {
numbers[left] = numbers[right];
left++; } while ((numbers[left] <= pivot) && (left < right))
left++;
if (left != right) {
numbers[right] = numbers[left]; right--;
} } numbers[left] = pivot;
pivot = left;
left = l_hold;
right = r_hold;
if (left < pivot) q_sort(numbers, left, pivot-1);
if (right > pivot) q_sort(numbers, pivot+1, right); }
6
Demo Quick Sort
• http://www.digsys.se/js_qsort.html
• http://home.att.net/~srschmitt/quick_sort.ht
ml
• http://ciips.ee.uwa.edu.au/~morris/Year2/P
LDS210/qsort.html
7
Efisiensi Quick Sort
8
Merge Sort
• The merge sort splits the list to be sorted into
two equal halves, and places them in separate
arrays. Each array is recursively sorted, and
then merged back together to form the final
sorted list. Like most recursive sorts, the merge
sort has an algorithmic complexity of O(n log n).
• Elementary implementations of the merge sort
make use of three arrays - one for each half of
the data set and one to store the sorted list in.
The below algorithm merges the arrays in-place,
so only two arrays are required.
9
Merge Sort
Like quicksort, merge sort uses recursion.
The basic idea is as follows:
• divide the array at its midpoint, and
recursively apply merge sort to both
halves.
• make a single pass through both halves
(which are now sorted), and merge them
into one sorted whole.
10
Merge Sort
void mergeSort(int numbers[], int temp[], int array_size) {
m_sort(numbers, temp, 0, array_size - 1);
}
void m_sort(int numbers[], int temp[], int left, int right) {
int mid;
if (right > left) {
mid = (right + left) / 2; m_sort(numbers, temp, left, mid);
m_sort(numbers, temp, mid+1, right);
merge(numbers, temp, left, mid+1, right);
}}
11
Merge Sort
void merge(int numbers[], int temp[], int left, int mid, int right) {
int i, left_end, num_elements, tmp_pos;
left_end = mid - 1;
tmp_pos = left;
num_elements = right - left + 1;
while ((left <= left_end) && (mid <= right)) {
if (numbers[left] <= numbers[mid]) {
temp[tmp_pos] = numbers[left];
tmp_pos = tmp_pos + 1; left = left +1;
} else { temp[tmp_pos] = numbers[mid];
tmp_pos = tmp_pos + 1; mid = mid + 1;
}}
12
Merge Sort
while (left <= left_end) {
temp[tmp_pos] = numbers[left];
left = left + 1;
tmp_pos = tmp_pos + 1;
}
while (mid <= right) { temp[tmp_pos] = numbers[mid]; mid
= mid + 1;
tmp_pos = tmp_pos + 1;
} for (i=0; i <= num_elements; i++) {
numbers[right] = temp[right]; right = right - 1; } }
13
Demo Mergesort
• http://max.cs.kzoo.edu/~abrady/java/sortin
g/MergeSort.html
• http://www.geocities.com/SiliconValley/Pro
gram/2864/File/Merge1/mergesort.html
14
Efisiensi Merge Sort
15
Penutup
• Quick sort merupakan teknik sort yang
mudah dan cepat.
16