l01-intro (3).ppt
- 1. The Design and Analysis of Algorithms by Anany Levitin Lecture notes prepared by Lydia Sinapova, Simpson College
- 2. 2 CHAPTER 1: INTRODUCTION What is an Algorithm Steps in Designing and Implementing an Algorithm Important Problem Types Fundamental Data Structures
- 3. 3 ALGORITHM A sequence of unambiguous instructions for solving a problem, i.e. for obtaining the required output for any legitimate input in a finite amount of time
- 4. 4 Important points Non-ambiguity Range of inputs The same algorithm can be represented in different ways Several algorithms for solving the same problem
- 5. 5 gcd(m,n) while n ≠0 do r ← m mod n m ← n n ← r return m 1. t ← min (m ,n) 2. if m % t = 0 goto 3, else goto 4 3. if n % t = 0 return t, else goto 4 4. t ← t - 1 5. goto 2
- 6. 6 Understand the problem Decide on computational means Exact vs approximate solution Data structures Algorithm design technique Design an algorithm Prove correctness Analyze the algorithm Code the algorithm
- 7. 7 What does it mean to understand the problem? What are the problem objects? What are the operations applied to the objects? Deciding on computational means How the objects would be represented? How the operations would be implemented?
- 8. 8 Design an algorithm • Build a computational model of the solving process Prove correctness • Correct output for every legitimate input in finite time • Based on correct math formula • By induction
- 9. 9 Analyze the algorithm Efficiency: time and space Simplicity Generality: range of inputs, special cases Optimality: no other algorithm can do better Coding How the objects and operations in the algorithm are represented in the chosen programming language?
- 10. 10 Important problem types Sorting Searching String processing Graph problems Combinatorial problems Geometric problems Numerical problems
- 11. 11 Fundamental data structures Linear data structures Array Linked list Stack Queue Operations: search, delete, insert Implementation: static, dynamic
- 12. 12 Non-linear data structures Graphs Trees : connected graph without cycles Rooted trees Ordered trees Binary trees Graph representation: adjacency lists, adjacency matrix Tree representation: as graphs; binary nodes Fundamental data structures
- 13. 13 Fundamental data structures Sets, Bags, Dictionaries Set: unordered collection of distinct elements Operations: membership, union, intersection Representation: bit string; linear structure Bag: unordered collection, elements may be repeated Dictionary: a bag with operations search, add, delete
- 14. 14 Conclusion Algorithm classification By types of problems By design technique Design techniques a general approach to solving problems