COS 121

• Problem


  An unpleasant situation or condition which a better or perfect state is desired
• Present state


  The current situation
• Goal state


  The desired state to be reached
• Types of problems


  • Routine problems
  • Non-routine problems
• Routine problems


  Problems with simple, predictable solutions
• Non-routine problems


  Problems with subjective, abstract and complex solutions
• Problem solving


  The application of ideas, skills, or factual information as inputs in specific sequence of steps to attain to the solution to a problem or to reach a desired goal state
• Solution


  The sequence of steps to solve a problem
• One problem can have multiple solutions
• Not all problems have straightforward solutions, some require trial and error
• Algorithmic solution


  Solutions to problems in which the desired state is achieved by a defined and finite sequence of steps
• Heuristic solution


  Solutions to problems in which the goal state is reached by series of steps which emerge from knowledge, experience and trial and error
• This course focuses on algorithmic solutions that can be solved by computers
• Solution techniques


  • Abstraction
  • Analogy
  • Brainstorming
  • Trial-and-error
  • Hypothesis testing
  • Reduction
  • Divide and Conquer
  • Lateral thinking
  • Means-ends analysis
  • Method of focal objects
  • Morphological analysis
  • Research
  • Root cause analysis
  • Proof
• Computers are built to deal with algorithmic solutions, which are often difficult or very time consuming for humans
• Humans can arrive at heuristic solutions better than computers
• The field of computer science that deals with heuristic problems is called Artificial Intelligence (AI)
• Steps of problem solving

  • Identify the problem
  • Understand the problem
  • Identify alternative solutions
  • Select the best solution
  • List instructions for the solution
  • Evaluate the solution
• Algorithm


  Shows the sequence of instructions comprising the solution to a problem
• Flowchart


  A graphical representation of an algorithm
• Pseudo code


  An informal human language-like description of the algorithm (steps) to arrive at a solution
• Designing an Algorithm


  1. Identify the Inputs (I)

  2. Identify the Process (P)

  3. Identify the Output (O)
• Characteristics of an Algorithm

  • Emphasize on the 'what' and not the 'how'
  • Each step must be exact
  • Must begin and terminate
  • Must be effective
  • Must be general
• Problem 1


  • Calculate the gross pay of an employee given the hours worked and the rate of pay
• Algorithm Design for Problem 1

  1. Input Hours, PayRate

  2. Calculate the GrossPay by multiplying Hours by PayRate

  3. Output the GrossPay
• The Algorithm for Problem 1
• Flowchart


  A graphical representation of an algorithm that shows the logic and sequence of steps
• Flowchart Symbols


  • Flow lines
  • Start/End
  • Processing block
  • Input/Output
  • Decision
  • Modules
  • Loop
  • On-page connector
  • Off-page connector
• Uses of Flowcharts


  • Facilitate communication
  • Play a vital role in programming
  • Helpful for understanding complicated problems
  • Ease of writing programs
• Rules for drawing Flowcharts
• Pseudo code


  1. A plain language description of the steps in an algorithm

  2. Similar to algorithm but more condensed

  3. Closer to programming language
• Differences between Algorithm and Pseudo code
• Pseudo code for Problem 1

  1. Input Hours, PayRate

  2. Calculate the GrossPay: GrossPay = Hours * PayRate

  3. Display the GrossPay
• Problem 2: Determine the VOLUME of a sphere


  1. Input Sphere Radius (r)

  2. Compute the Volume (V) using formula: V = (4/3) *pi*r3

  3. Display the Volume (V)
• Problem 3: Convert temperature in Degrees Celsius (oC) to Degrees Fahrenheit (oF)

  1. Input Temperature value (oC)

  2. Convert to temperature value (oF) using formula: F = (9/5)*C+32

  3. Display temperature value (oF)