algorithms and practice

1. CSCI 101
Algorithms II
Elsayed Hemayed

2. Overview
• Multiplication table
• Matrix multiplication
• Sorting
• Practice Problems

3. Displaying the multiplication table
for i=1:5
for j=1:5
fprintf(‘%8d’,i*j);
end
fprintf(‘n’);
end 1 2 3 4 5
2 4 6 8 10
3 6 9 12 15
4 8 12 16 20
5 10 15 20 25

4. Displaying a modified multiplication table
for i=1:5
for j=i:5
fprintf(‘%8d’,i*j);
end
fprintf(‘n’);
end 1 2 3 4 5
4 6 8 10
9 12 15
16 20
25

5. Matrices Multiplication
• Given matrix A [n][k] and matrix B[k][m] find
their multiplication matrix C[n][m].
i
j
i
a
a
j
=x
A [n][k] B[k][m] C[n][m]

6. Matrices Multiplication
for i =1 to n
for j=1 to m
C[i][j]=0
for a=1 to k
C[i][j]=C[i][j]+A[i][a]*B[a][j]
i
j
i
a
a
j
=x

7. Sorting
• Given a list of N integer values, sort them in an
ascending order.
for i=1 to N
for j=i+1 to N
If A[i]>A[j]
swap A[i] and A[j]
5
4
2
1
6

8. Array Sorting
X=input(‘enter an array:’);
for i=1:length(X)
for j=i+1:length(X)
if X(i)>X(j)
t=X(i);
X(i)=X(j);
X(j)=t;
end
end
end
disp(X);
5
4
2
1
6
4
5
2
1
6
2
5
4
1
6
1
5
4
2
6
i=1
j= 2 3 4 5
1
5
4
2
6
enter an array: [5 4 2 1 6]
Swapping values

9. What is the output of this program?
N=input(‘enter a number:’);
for i=1:N
for j=1:i
fprintf(‘*’);
end
fprintf(‘n’);
end
Enter a number: 5
*
**
***
****
*****

10. Practice Problems

11. Problem 1
Write a program that reads a number N from the
user and prints an array containing the numbers
(from 1 to N) that are multiples of 3 or 5
Also print their sum
Input/Output Sample:
Enter number: 10
The array that has multiples of 3 or 5 = 3 5 6 9 10
The sum of the multiples of 3 or 5 = 33

12. Problem 2
N children at a party eat scoops of ice cream, write a matlab program
to calculate how many scoops of ice cream do they eat altogether and
who eats more, if the user enters a negative number, the program asks
the user to re-enter the number.
Input/Output Sample:
Enter the number of children: 4
Enter number of scoops/ child: 1
Enter number of scoops/ child: -2
Error! Enter Positive Number: 4
Enter number of scoops/ child: 5
Enter number of scoops/ child: 3
Number of ice cream scoops all children ate: 13
Child ate more ice scoops: 3

13. Problem 3
In train station, the price of ticket depends on the destination
distance. There is a 20% discount for prices>160, 5% for
prices<100 and 10% for any other prices.
Write a matlab script to print final price for each station.
The program can be executed 3 times.
Input/Output Sample:
Enter tickets price/station: [150 210 50 75 80 170]
Discounted prices are: 135.00 168.00 47.50 71.25 76.00 136.00

14. Problem 4
Write MATLAB code that reads an array from user and
counts the number of elements that have values between
50 and 90 and calculates the max, and average of these
numbers. If the array does not contain numbers in the
required range the program should display “there are no
numbers between 50, 90 in the array”
Input/Output Sample:
Enter your array of numbers: [2 3 55 88 65 57 99 78]
Count of numbers between 50, 90 is: 5
Max is: 88
Avg is: 68.6

15. Problem 5
A customer want to buy a TV at least price. Write a program to help
him to know the average price of the TV and the store at which the
least price. The program should ask the customer about the number of
stores that have the required TV, and he should then enter the TV
price at each store. Then the program should print the average price of
TV in all stores, and where the least price.
Input/Output Sample:
Enter the number of stores have the required TV: 4
Enter the price of the TV in this store: 2800
Enter the price of the TV in this store: 2780
Enter the price of the TV in this store: 2930
Enter the price of the TV in this store: 2855
The average price of TV in all stores: 2841.25
The store have the least TV price: 2