Sorting
Background
• As soon as you create a significant database, you’ll
probably think of reasons to sort it in various ways. You
need to arrange names in alphabetical order, students by
grade, customers by ZIP code, home sales by price, cities
in order of increasing population, countries by GNP,
stars by magnitude, and so on.
• Sorting data may also be a preliminary step to searching
it. As we saw in “Arrays,” a binary search, which can be
applied only to sorted data, is much faster than a linear
search.
• Imagine that your kids-league baseball team is lined up on the
field, as shown in Figure 3.1. The regulation nine players, plus
an extra, have shown up for practice. You want to arrange the
players in order of increasing height (with the shortest player
on the left) for the team picture. How would you go about this
sorting process?
• As a human being, you have advantages over a
computer program.
▫ You can see all the kids at once, and you can pick out the tallest
kid almost instantly. You don’t need to laboriously measure and
compare everyone.
▫ Also, the kids don’t need to occupy particular places. They can
jostle each other, push each other a little to make room, and stand
behind or in front of each other. After some ad hoc rearranging,
you would have no trouble in lining up all the kids.
Bubble Sort
• The bubble sort is notoriously slow, but it’s
conceptually the simplest of the sorting
algorithms and for that reason is a good
beginning for our exploration of sorting
techniques.
• Bubble Sort on the Baseball Players
1. Compare two players.
2. If the one on the left is taller, swap them.
3. Move one position right.
Kondisi Awal
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Perulangan outer: 9
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Perulangan outer: 8
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Perulangan outer: 7
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Perulangan outer: 6
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Perulangan outer: 5
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Perulangan outer: 4
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Perulangan outer: 3
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Perulangan outer: 2
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Selection Sort
• The selection sort improves on the bubble sort by reducing
the number of swaps. Unfortunately, the number of
comparisons remains the same.
• However, the selection sort can still offer a significant
improvement for large records that must be physically moved
around in memory, causing the swap time to be much
more important than the comparison time.
• What’s involved in the selection sort is making a pass through
all the players and selecting the shortest one. This
shortest player is then swapped with the player on the
left end of the line, at position 0. Now the leftmost player
is sorted and won’t need to be moved again.
• Notice that in this algorithm the sorted players accumulate on
the left (lower indices), whereas in the bubble sort they
accumulated on the right.
• The next time you pass down the row of players, you start at
position 1, and, finding the minimum, swap with position 1.
This process continues until all the players are sorted.
Kondisi Awal
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Perulangan outer: 0
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Perulangan outer: 1
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Perulangan outer: 2
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Perulangan outer: 3
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4
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Perulangan outer: 4
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Perulangan outer: 5
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Perulangan outer: 6
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Perulangan outer: 7
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Perulangan outer: 8
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Insertion Sort
• In most cases the insertion sort is the best of the elementary
sorts described in this chapter. It’s about twice as fast as the
bubble sort and somewhat faster than the selection sort in
normal situations.
• Insertion Sort on the Baseball Players
• To begin the insertion sort, start with your baseball players
lined up in random order.
• It’s easier to think about the insertion sort if we begin in the
middle of the process, when the team is half sorted.
• What we’re going to do is insert the marked player in the
appropriate place in the (partially) sorted group. However, to
do this, we’ll need to shift some of the sorted players to the
right to make room. To provide a space for this shift, we take
the marked player out of line. (In the program this data item
is stored in a temporary variable.)
Kondisi Awal
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Perulangan outer: 1
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Temp
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Perulangan outer: 2
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Temp
55
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Perulangan outer: 3
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Temp
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Perulangan outer: 4
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Temp
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Perulangan outer: 5
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Temp
22
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88
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66
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88
Perulangan outer: 6
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Temp
11
22
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66
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11
Perulangan outer: 7
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Perulangan outer: 8
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66
Perulangan outer: 9
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Temp
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Sorting Objects
Comparing the Simple Sorts
• The bubble sort is so simple that you can write it
from memory. Even so, it’s practical only if the
amount of data is small.
• The selection sort minimizes the number of swaps,
but the number of comparisons is still high. This
sort might be useful when the amount of data is
small and swapping data items is very timeconsuming compared with comparing them.
• The insertion sort is the most versatile of the three
and is the best bet in most situations, assuming the
amount of data is small or the data is almost sorted.