Matakuliah
Tahun
Versi
: T0016/Algoritma dan Pemrograman
: 2005
: versi 2
Pertemuan 22
Radix Sort
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Learning Outcomes
Pada akhir pertemuan ini, diharapkan mahasiswa
akan mampu :
• Menjelaskan teknik radix sort
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Outline Materi
• Pengenalan radix sort
3
Radix Sort
Definition :
• A multiple pass distribution sort algorithm
that distributes each item to a bucket
according to part of the item's key
beginning with the least significant part of
the key. After each pass, items are
collected from the buckets, keeping the
items in order, then redistributed according
to the next most significant part of the key.
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Radix Sort
•
Here is a simple example of the sort. Suppose the input keys are 34, 12, 42,
32, 44, 41, 34, 11, 32, and 23.
•
Four buckets are appropriate. The first pass distributes them by the least
significant digit. After the first pass we have the following, where each line is
a bucket.
41 11
12 42 32 32
23
34 44 34
•
We collect these, keeping their relative order: 41 11 12 42 32 32 23 34 44
34. Now we distribute by the next most significant digit, in this case, the
highest digit, and we get the following.
11 12
23
32 32 34 34
41 42 44
When we collect them, they are in order: 11 12 23 32 32 34 34 41 42 44.
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Contoh
void radix (int byte, long N, long *source, long *dest) {
long count[256]; long index[256];
memset (count, 0, sizeof (count));
for ( int i=0; i<N; i++ ) count[((source[i])>>(byte*8))&0xff]++;
index[0]=0; for ( i=1; i<256; i++ ) index[i]=index[i-1]+count[i-1];
for ( i=0; i<N; i++ ) dest[index[((source[i])>>(byte*8))&0xff]++] = source[i];
}
void radixsort (long *source, long *temp, long N) {
radix (0, N, source, temp);
radix (1, N, temp, source);
radix (2, N, source, temp);
radix (3, N, temp, source);
}
void make_random (long *data, long N) {
for ( int i=0; i<N; i++ ) data[i]=rand()|(rand()<<16);
}
long data[100];
long temp[100];
void main (void) {
make_random(data, 100);
radixsort (data, temp, 100);
for ( int i=0; i<100; i++ ) cout << data[i] << '\n'; }
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LSD Radix Sort
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Contoh MSD Radix Sort
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Penutup
Radix Sort makes several passes of the
previous Counting Sort in order to
completely sort integer keys. Counting
Sort can be used as the intermediate
sorting routine because it provides a
stable sort.
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