Lecture 3Algorithms Part I

Calculating sum and average, Getting the maximum, Counting occurrences,

Finding matches

Overview

• Calculating sum & average of students’ grades

• Getting the maximum

• Counting number of zeroes

• Finding locations of zeroes

• Counting number of occurrences

• Finding the matched elements

One Dimension Arrays

X= [4 5 2 6 8]

length(X): number of elements

To access the array elements use for-loop.

for i=1:length(X) % use X(i)

end

4

5

2

6

8

X(1)

X(2)

X(3)

X(4)

X(5)

Calculate sum & average of students’ grades (Program and Testing)

X=input(‘enter student grades:’);sum=0;for i=1:length(X)

sum=sum+X(i);endavg = sum/length(X);disp(sum);disp(avg);

i X(i) sum

0

1 8 8

2 7 15

3 9 24

4 5 29

5 6 35

enter student grades: [8 7 9 5 6]

Getting the maximum (Problem & Algorithm)

• Given N numbers, find their maximum value

[3 5 -2 7 1] has a maximum value 7

Algorithm- Get N numbers- Assume max value = 0- Make a for loop from 1 to N

In every iteration, get one number xif x is greater than my max then replace my max

- Display my max

Getting the maximum (Program)

X=input(‘enter elements:’);max=0;for i=1:length(X)

if X(i)>maxmax=X(i);

endenddisp(max);

i X(i) max

0

1 3 3

2 5 5

3 -2 5

4 7 7

5 1 7

enter elements: [3 5 -2 7 1]

Getting the maximum and its index (Program)

X=input(‘enter elements:’);max=0;for i=1:length(X)

if X(i)>maxmax=X(i);maxi = i;

endenddisp(max);disp(maxi);

i X(i) max maxi

0

1 3 3 1

2 5 5 2

3 -2 5 2

4 7 7 4

5 1 7 4

enter elements: [3 5 -2 7 1]

Counting number of zeroes I (Problem)

• Given a list of values, count how many zeroes is found in the list.

• Example 1:

– Input: [6 0 12 0 12]

– Output: 2

• Example 2:

– Input: [6 5 12 14 10]

– Output: 0

Counting number of zeroes I(Algorithm)

- Get N elements

- Set count=0

- Make a for loop from 1 to N

In every iteration, get one number x

if x equal zero then increment count

- Print count

Counting number of zeroes I(Program)

X=input(‘enter elements:’);

count=0;

for i=1:length(X)

if X(i)==0

count=count+1;

end

end

disp(count);

i X(i) count

0

1 6 0

2 0 1

3 12 1

4 0 2

5 12 2

enter elements: [6 0 12 0 12]

Counting number of zeroes II (Problem)

• Given a list of values, count how many zeroes is found in the list. If not found then print “Not Found”

• Example 1: – Input: [6 0 12 0 12]

– Output: 2

• Example 2: – Input: [6 5 12 14 10]

– Output: Not Found

Counting number of zeroes II (Algorithm)

- Get N elements

- Set count=0

- Make a for loop from 1 to N

In every iteration, get one number x

if x equal zero then increment count

- if count >0 then print count

Otherwise print ‘Not Found’

Counting number of zeroes II(Program)

X=input(‘enter elements:’);count=0;for i=1:length(X)

if X(i)==0count=count+1;

endendIf count > 0

disp(count);else

disp(‘Not Found’);end

enter elements: [6 0 12 0 12]

i X(i) count

0

1 6 0

2 0 1

3 12 1

4 0 2

5 12 2

Counting number of zeroes II(Program)

X=input(‘enter elements:’);

count=0;

for i=1:length(X)

if X(i)==0

count=count+1;

end

end

If count > 0

disp(count);

else

disp(‘Not Found’);

end

i X(i) count

0

1 6 0

2 5 0

3 12 0

4 14 0

5 12 0

enter elements: [6 5 12 14 12]

Counting number of occurrence (Problem)

• Given a list of values and a key, count how many times the key is found in the list. If not found then print “Not Found”

• Example 1: – Input: [6 5 12 14 12] and key=12

– Output: 2

• Example 2: – Input: [6 5 12 14 10] and key=7

– Output: Not Found

Counting number of occurrence(Algorithm)

- Get the key

- Get N elements

- Set count=0

- Make a for loop from 1 to N

In every iteration, get one number x

if x equal key then increment count

- if count >0 then print countOtherwise print ‘Not Found’

Counting number of occurrence (Program)

Key=input(‘enter the key:’);X=input(‘enter elements:’);count=0;for i=1:length(X)

if X(i)==keycount=count+1;

endendIf count > 0

disp(count);else

disp(‘Not Found’);end

i X(i) count

0

1 6 0

2 5 0

3 12 1

4 14 1

5 12 2

enter the key: 12enter elements: [6 5 12 14 12]

Counting number of occurrence (Program)

Key=input(‘enter the key:’);X=input(‘enter elements:’);count=0;for i=1:length(X)

if X(i)==keycount=count+1;

endendIf count > 0

disp(count);else

disp(‘Not Found’);end

i X(i) count

0

1 6 0

2 5 0

3 12 0

4 14 0

5 12 0

enter the key: 7enter elements: [6 5 12 14 12]

Finding the matched elements (Problem)

• Given a list of values and a key, check if the key is found in the list and print the locations of these match otherwise, print Not Found.

• Example 1: – Input: [6 5 12 14 12] and key=12

– Output: 3

5

• Example 2: – Input: [6 5 12 14 12] and key=7

– Output: Not Found

Finding the matched elements (Algorithm)

- Get the key

- Get N elements

- Make a for loop from 1 to N

In every iteration, get one number x

if x equal key then display the iteration number

- If the key is not found then print “not Found”

Finding the matched elements (Program)

Key=input(‘enter the key:’);X=input(‘enter elements:’);count=0;for i=1:length(X)

if X(i)==keydisp(i);count=count+1;

endendif count==0

disp(‘Not Found’);end

i X(i) count

0

1 6 0

2 5 0

3 12 1

4 14 1

5 12 2

enter the key: 12enter elements: [6 5 12 14 12]35

Finding the matched elements (Program)

Key=input(‘enter the key:’);X=input(‘enter elements:’);count=0;for i=1:length(X)

if X(i)==keydisp(i);count=count+1;

endendif count==0

disp(‘Not Found’);end

i X(i) count

0

1 6 0

2 5 0

3 12 0

4 14 0

5 12 0

enter the key: 7enter elements: [6 5 12 14 12]Not Found

Thank You

Course Site: http://scholar.cu.edu.eg/?q=eldeib/classes/genn004-computers-engineers

Computers for Engineers – GENN004