Location: Academic Organisations » OpenCourseWare Consortium » MIT OpenCourseWare » MIT 6.046J / 18.410J Introduction to Algorithms - Fall 2005

Lecture 4: Quicksort, Randomized Algorithms

author: Charles E. Leiserson, Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, MIT
recorded by: Massachusetts Institute of Technology, MIT
published: Feb. 10, 2009,   recorded: September 2005,   views: 12840
released under terms of: CC BY-NC-SA
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Slides

Slides
0:00 Introduction to Algorithms - Lecture 4
0:16 Quicksort
2:15 Divide and conquer
5:17 Partitioning subroutine
11:39 Example of partitioning (1)
12:26 Example of partitioning (2)
12:30 Example of partitioning (2)
12:37 Example of partitioning (3)
12:57 Example of partitioning (4)
13:02 Example of partitioning (5)
13:09 Example of partitioning (6)
13:24 Example of partitioning (7)
14:32 Example of partitioning (8)
14:47 Example of partitioning (9)
14:57 Example of partitioning (10)
15:15 Example of partitioning (11)
15:55 Pseudocode for quicksort
18:57 Analysis of quicksort
20:53 Worst-case of quicksort
24:16 Worst-case recursion tree (1)
24:37 Worst-case recursion tree (2)
24:43 Worst-case recursion tree (3)
25:11 Worst-case recursion tree (4)
25:36 Worst-case recursion tree (5)
26:15 Worst-case recursion tree (6)
26:20 Worst-case recursion tree (7)
28:43 Best-case analysis
33:29 Analysis of "almost-best"case (1)
33:35 Analysis of "almost-best"case (2)
33:47 Analysis of "almost-best"case (3)
34:49 Analysis of "almost-best"case (4)
36:44 Analysis of "almost-best"case (5)
41:16 More intuition
46:31 Randomized quicksort
51:05 Randomized quicksort analysis (1)
57:48 Randomized quicksort analysis (2)
60:54 Calculating expectation (1)
61:57 Calculating expectation (2)
63:08 Calculating expectation (3)
65:01 Calculating expectation (4)
67:05 Calculating expectation (5)
68:22 Hairy recurrence
74:57 Substitution method (1)
76:13 Substitution method (2)
76:58 Substitution method (3)
78:07 Substitution method (4)
79:08 Quicksort in practice

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"OK. Today we are going to talk about a very interesting algorithm called Quicksort -- -- which was invented by Tony Hoare in 1962. And it has ended up being a really interesting algorithm from many points of view. And because of that, it turns out today's lecture is going to be both hard and fast. If you see the person next to you sleeping, you will want to say let's get going. It's a divide-and-conquer algorithm..."

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Comment6 vikram chauhan, August 8, 2011 at 8:52 p.m.:

want to know the quick sort

Comment7 Pap , January 16, 2013 at 11 p.m.:

Very nice video. Thanks professor for such a nice explanation.

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