1 Algorithms and Problem Solving

2 Outline  Problem Solving  Problem Solving Strategy  Algorithms  Sequential Statements  Examples

3 Problem Solving  Solving a problem means that we know the way or the method to follow manually from the start till the end.  Having the method known, the same method is used by the computer to solve the problem but faster with higher precision.  If we do not know how to solve a problem ourselves, the computer will not be of any help in this regard.  The strategy for solving a problem goes through the following stages:  Analysis: in this stage, we should find what the problem should do.  Design : the way or method of how your problem is solved is produced  Implementation: the method found in design is then coded here in a given programming language.  Testing: here we verify that the program written is working correctly  Deployment : finally the program is ready to use

4 Problem Solving Strategy

5 Algorithms  An algorithm is a sequence of instructions that solve a problem with the following properties:  No ambiguity in any instruction  No ambiguity which instruction is next  Finite number of instructions  Execution must halt  The description of the instructions can be given in English like statements called pseudo-code  The flow control of instructions has three types:  Sequential  Selection  Iteration

6 Sequential Statements  Instructions in this type are executed one after the other in sequence  These statements include:  Assignment statement  Method calls

7 Example1  Write a program that assigns the Cartesian coordinates of two points (x1, y1) and (x2, y2) and displays the distance between them using the following formula.  Algorithm: »x1 = 1 »y1 = 1 »x2 = 4 »y2 = 6 »distance = sqrt( (x2 – x1) ^ 2 + (y2 – y1) ^ 2 ) »print distance

8 Example1 (cont'd)  Java code: public class Distance { public static void main(String[] args) { double x1, y1, x2, y2, dist; x1 = 1.0; y1 = 1.0; x2 = 4.0; y2 = 6.0; dist = Math.sqrt(Math.pow(x2-x1,2)+ Math.pow(y2-y1,2)); System.out.println("The distance is " + dist); }

9 Example2  Write a program that finds the area of a triangle given the length of its sides: a, b, c. Use a = 3, b = 4, c = 5 to test your solution.  Algorithm: »a = 3 »b = 4 »c = 5 »s = (a + b + c) / 2 »area = sqrt( s* (s – a) * (s – b) * (s – c) ) »print area

10 Example2 (cont'd)  Java code: public class Distance { public static void main(String[] args) { double a, b, c, area; a = 3.0; b = 4.0; c = 5.0; s = (a + b + c ) / 2.0; area = Math.sqrt(s * (s - a) * (s – b) * (s – c) ); System.out.println("The area is " + area); }