Introduction to Problem Solving Class 11 Notes | CBSE Computer Science

Latest Problem Solving Class 11 Notes includes Problem Solving, steps, algorithm and its need, flow chart, pseudo code with lots of examples.

What is Problem Solving?

Problem solving is the process of identifying a problem, analyze the problem, developing an algorithm for the identified problem and finally implementing the algorithm to develop program.

Steps for problem solving

There are 4 basic steps involved in problem solving

• Analyze the problem
• Developing an algorithm
• Coding
• Testing and debugging

Analyze the problem

Analyzing the problem is basically understanding a problem very clearly before finding its solution. Analyzing a problem involves

• List the principal components of the problem
• List the core functionality of the problem
• Figure out inputs to be accepted and output to be produced

Developing an Algorithm

• A set of precise and sequential steps written to solve a problem
• The algorithm can be written in natural language
• There can be more than one algorithm for a problem among which we can select the most suitable solution.

Coding

Algorithm written in natural language is not understood by computer and hence it has to be converted in machine language. And to do so program based on that algorithm is written using high level programming language for the computer to get the desired solution.

Testing and Debugging

After writing program it has to be tested on various parameters to ensure that program is producing correct output within expected time and meeting the user requirement.

There are many standard software testing methods used in IT industry such as

• Component testing
• Integration testing
• System testing
• Acceptance testing

What is Algorithm?

• A set of precise, finite and sequential set of steps written to solve a problem and get the desired output.
• Algorithm has definite beginning and definite end.
• It lead to desired result in finite amount of time of followed correctly.

Why do we need Algorithm?

• Algorithm helps programmer to visualize the instructions to be written clearly.
• Algorithm enhances the reliability, accuracy and efficiency of obtaining solution.
• Algorithm is the easiest way to describe problem without going into too much details.
• Algorithm lets programmer understand flow of problem concisely.

Characteristics of a good algorithm

• Precision — the steps are precisely stated or defined.
• Uniqueness — results of each step are uniquely defined and only depend on the input and the result of the preceding steps.
• Finiteness — the algorithm always stops after a finite number of steps.
• Input — the algorithm receives some input.
• Output — the algorithm produces some output.

What are the points that should be clearly identified while writing Algorithm?

• The input to be taken from the user
• Processing or computation to be performed to get the desired result
• The output desired by the user

Representation of Algorithm

An algorithm can be represented in two ways:

• Flow chart
• Pseudo code

Flow chart

• Flow chart is visual representation of an algorithm.
• It’s a diagram made up of boxes, diamonds and other shapes, connected by arrows.
• Each step represents a step of solution process.
• Arrows in the follow chart represents the flow and link among the steps.

Flow Chart Examples

Example 1: Write an algorithm to divide a number by another and display the quotient.

Input: Two Numbers to be divided
Process: Divide number1 by number2 to get the quotient
Output: Quotient of division

Algorithm

Step 1: Input a two numbers and store them in num1 and num2
Step 2: Compute num1/num2 and store its quotient in num3
Step 3: Print num3

Flow chart

Pseudo code

• Pseudo code means ‘not real code’.
• A pseudo code is another way to represent an algorithm.  It is an informal language used by programmer to write algorithms.
• It does not require strict syntax and technological support.
• It is a detailed description of what algorithm would do.
• It is intended for human reading and cannot be executed directly by computer.
• There is no specific standard for writing a pseudo code exists.

Keywords used in writing pseudo code

• INPUT
• COMPUTE
• PRINT
• INCREMENT
• DECREMENT
• IF/ELSE
• WHILE
• TRUE/FALSE

Pseudo Code Example

Example:  write an algorithm to display the square of a given number.

Input, Process and Output Identification

Input: Number whose square is required
Process: Multiply the number by itself to get its square
Output: Square of the number

Algorithm

Step 1: Input a number and store it to num.
Step 2: Compute num * num and store it in square.
Step 3: Print square.

Pseudo code

INPUT num
COMPUTE  square = num*num
PRINT square

Flow chart

Example: Write an algorithm to calculate area and perimeter of a rectangle, using both pseudo code and flowchart.

Pseudo code

INPUT L
INPUT B
COMPUTER Area = L * B
PRINT Area
COMPUTE Perimeter = 2 * ( L + B )
PRINT Perimeter

Flow Chart

Flow of Control

An algorithm is considered as finite set of steps that are executed in a sequence. But sometimes the algorithm may require executing some steps conditionally or repeatedly. In such situations algorithm can be written using

• Sequence
• Selection
• Repetition

Selection

Selection in algorithm refers to Conditionals which means performing operations (sequence of steps) depending on True or False value of given conditions. Conditionals are written in the algorithm as follows:

If <condition> then
                Steps to be taken when condition is true
Otherwise
                Steps to be taken when condition is false

Algorithm, Pseudocode, Flowchart with Selection ( Using if ) Examples

Example: write an algorithm, pseudocode and flowchart to display larger between two numbers

Input, Process and Output Identification

INPUT: Two numbers to be compared
PROCESS: compare two numbers and depending upon True and False value of comparison display result
OUTPUT: display larger no

Algorithm

STEP1: read two numbers in num1, num2
STEP 2: if num1 > num2 then
STEP 3: display num1
STEP 4: else
STEP 5: display num2

Pseudo code

INPUT num1 , num2
IF num1 > num2 THEN
                PRINT “num1 is largest”
ELSE
                PRINT “num2 is largest”
ENDIF

Flow Chart

Example: write pseudocode and flowchart to display largest among three numbers

Input, Process and Output Identification

INPUT: Three numbers to be compared
PROCESS: compare three numbers and depending upon True and False value of comparison display result
OUTPUT: display largest number

Pseudocode

INPUT num1, num2, num3
PRINT “Enter three numbers”
IF num1 > num2 THEN
                IF num1 > num3 THEN
                                PRINT “num1 is largest”
                ELSE
                                PRINT “num3 is largest”
                END IF
ELSE
                IF num2 > num3 THEN
                                PRINT “num2 is largest”
                ELSE
                                PRINT “num3 is largest”
                END IF
END IF

Flow chart

Repetition

• Repetition in algorithm refers to performing operations (Set of steps) repeatedly for a given number of times (till the given condition is true).
• Repetition is also known as Iteration or Loop

Repetitions are written in algorithm is as follows:

While <condition>, repeat step numbers
                Steps to be taken when condition is true
End while

Algorithm, Pseudocode, Flowchart with Repetition ( Loop ) Examples

Example: write an algorithm, pseudocode and flow chart to display “Techtipnow” 10 times

Algorithm

Step1: Set count = 0
Step2: while count is less than 10, repeat step 3,4
Step 3:                  print “techtipnow”
Step 4:                  count = count + 1
Step 5: End while

Pseudocode

SET count = 0
WHILE count<10
                PRINT “Techtipnow”
                Count = count + 1
END WHILE

Flow chart

Example: Write pseudocode and flow chart to calculate total of 10 numbers

Pseudocode

Step 1: SET count = 0, total = 0
Step 2: WHILE count < 10, REPEAT steps 3 to 5
Step 3:                  INPUT a number in var
Step 4:                  COMPUTE total = total + var
Step 5:                  count = count + 1
Step 6: END WHILE
Step 7: PRINT total

Flow Chart

Example: Write pseudo code and flow chart to find factorial of a given number

Step 1: SET fact = 1
Step 2: INPUT a number in num
Step 3: WHILE num >=1 REPEAT step 4, 5
Step 4:                  fact = fact * num
Step 5:                  num = num – 1
Step 6: END WHILE
Step 7: PRINT fact

Flow chart

Decomposition

• Decomposition means breaking down a complex problem into smaller sub problems to solve them conveniently and easily.
• Breaking down complex problem into sub problem also means analyzing each sub problem in detail.
• Decomposition also helps in reducing time and effort as different subprograms can be assigned to different experts in solving such problems.
• To get the complete solution, it is necessary to integrate the solution of all the sub problems once done.

Following image depicts the decomposition of a problem