Introduction to the algorithm of "lecture notes"

Course Address

Http://v.163.com/special/opencourse/algorithms.html

Today's course Address:

Http://open.163.com/movie/2010/12/G/F/M6UTT5U0I_M6V2T1JGF.html

Discussion performance

Analysis of algorithms:the Study of computer program performance ans resource usage.

Thinking:what is more important than performance?

Functionality, modularity, user-friendliness, security ...

Then why study ALGs and perf?

Performance is like the ' money ', you can buy other stuff ... This is a little bit of a deal.

Problem sorting

Insertion Sort

Every time I make sure I'm in the first place, it's sort.

8 2 4 9 3 6 i = 1

2 8 4 9 3 6 i = 2

2 4 8 9 3 6 i = 3

2 4 8 9 3 6 i = 4

2 3 4 8 9 6 i = 5

2 3 4 6 8 9 done

Running Time Analysis

• Depends on input (best case, Wrost case)
• Depends on input size

Wrost case, Ave case, best case

Analysis of BIG IDEA:ASYMPTOTC

• Ignore Machine Dependent
• Look at the growth

Θnotation, compared to n in the case of infinite big ~ so n^2 certainly faster than n^3.

Wrost Case:

Θ (n^2)

Merge sort a[1,..., N]

1, if n =1, done

2, recursively sort a[1,..., N/2] and A[N/2 + 1, ..., n]

3, merge 2 sorted lists

T (n) = 2T (N/2) +θ (n) if n > 1

T (n) = Cn*lgn +θ (n) =θ (NLGN) c stands for constant

Introduction to the algorithm of "lecture notes"