Session 07 Introduction to Programming
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LBC, Session 7
Searching and Sorting
FPT APTECH COMPUTER EDUCATION HANOI
Objectives
•
Explain the need of searching and sorting
•
Discuss basic sorting algorithms:
– Bubble Sort
– Insertion Sort
•
Discuss basic searching algorithms:
– Linear Search
– Binary Search
LBC/Session 7
2
Sorting
• Sorting involves arranging the array
data in a specified order such as
ascending or descending
• Data in an array is easier to search
when the array is sorted
• Two of methods to sort arrays:
Selection Sort and Bubble Sort
LBC/Session 7
3
Sorting (cont’d)
• In the selection sort method, the
value present in each element is
compared with the subsequent
elements in the array to obtain the
least/greatest value
• There are 2 approaches in bubble
sort implementation:
Bottom-up
Top-down
LBC/Session 7
4
Bubble Sort
•
•
12
6
12
6
22
14
22
14
8
8
17
22
17
22
6
12
14
8
14
8
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For an array of n elements
Repeat these following steps n-1 times:
With a[i] and a[i+1]:
If a[i] greater than a[i+1] then swap there location.
LBC/Session 7
5
Bubble Sort
int i,j,temp,arr[5]={23,90,9,25,16};
for (int i=0; i<4; i++)
{
for (int j=0; j<5-i-1; j++)
{
if (arr[j] > arr[j+1])
{
int temp = arr[j];
arr[j] = arr[j+1];
arr[j+1] = temp;
}
}
}
LBC/Session 7
6
Insertion Sort
• Main Ideas for sorting using
Insertion Sort:
– For each element of the array, put it to the
‘right’ position between other sorted elements
– When the last element is put to the ‘right’
location, the array is sorted
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Insertion Sort
23
17
45
18
LBC/Session 7
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22
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Insertion Sort
23
17
45
18
12
22
1
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6
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Insertion Sort
23
17
45
18
12
22
1
2
3
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5
6
1
2
3
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5
6
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Insertion Sort
1
17
45
18
12
22
2
3
4
5
6
2
3
4
5
6
23
1
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Insertion Sort
1
2
17
23
1
2
45
18
12
22
3
4
5
6
3
4
5
6
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Insertion Sort
1
2
3
17
23
45
1
2
3
18
12
22
4
5
6
4
5
6
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Insertion Sort
1
2
3
4
17
18
23
45
1
2
3
4
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22
5
6
5
6
14
Insertion Sort
1
2
3
4
5
6
12
17
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23
45
1
2
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5
6
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15
Insertion Sort
int data[5] = { 23, 90, 9, 25, 16 };
int tmp,i,j;
//perform insertion sorting
for (j=1; j
tmp = data[j];
while ( (i>=0) && (tmp < data[i]) ) {
data[i+1] = data[i];
i--;
}
data[i+1] = tmp;
}
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16
Searching
For this lesson, we discuss two
kinds of searching:
• Linear search
• Binary search
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Linear Searching
This is the simplest way to find an
element in an array by visiting all
elements of the array until the item
is found
Also called Sequential searching
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18
Linear Searching
int data[] = {5,2,9,7,6,10};
int a = 7,i;
for(i = 0; i<6; i++){
if(a == data[i])
break;
}
if(i<6){
printf(“Number %d found at %d”,a,i);
}else{
printf(“Number not found”);
}
}
LBC/Session 7
19
Binary Searching
• Binary
Search
is
implemented
sorted arrays
• This algorithm uses recursion
implement searching:
on
to
Step 1: Compare item to search with the element in the
middle location of the array. If the comparison returns
equals, end searching
Step 2: If the comparison returns ‘less than’ repeat step
1 with the left-side part of the array
Step 3: If the comparison returns ‘greater than’ repeat
step 1 with the right-side part of the array
LBC/Session 7
20
Binary Searching - Example
Example: Find number 33 in the sorted array below:
6
0
13 14 25 33 43 51 53 64 72 84 93 95 96 97
1
2
3
4
5
6
7
8
lo
9
10
11
12
13
14
hi
LBC/Session 7
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Binary Searching - Example
Example: Find number 33 in the sorted
array below:
6
0
lo
13 14 25 33 43 51 53 64 72 84 93 95 96 97
1
2
3
4
5
6
7
8
mid
LBC/Session 7
9
10
11
12
13
14
hi
22
Binary Searching - Example
Example: Find number 33 in the
sorted array below:
6
0
lo
13 14 25 33 43 51 53 64 72 84 93 95 96 97
1
2
3
4
5
6
7
8
9
10
11
12
13
14
hi
LBC/Session 7
23
Binary Searching - Example
Example: Find number 33 in the
sorted array below:
6
0
lo
13 14 25 33 43 51 53 64 72 84 93 95 96 97
1
2
3
mid
4
5
6
7
8
9
10
11
12
13
14
hi
LBC/Session 7
24
Binary Searching - Example
Example: Find number 33 in the
sorted array below:
6
0
13 14 25 33 43 51 53 64 72 84 93 95 96 97
1
2
3
4
lo
5
6
7
8
9
10
11
12
13
14
hi
LBC/Session 7
25
