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05-K-02. Backward Analysis

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05-K-02. Backward Analysis课程教案、知识点、字幕

什么叫做backward analysis呢

实际上它是区别于

我们常用的那种前向分析

forward analysis

举个例子

比如我要来预测一下

明天股市的行情

明天的股票到底是会涨还是落呢

会涨多少 会落多少呢

如果我关注于此

我要做的事情

肯定会竭尽所能

去搜集各种各样可能获得的

与之相关的信息

然后可能会涉及一个

相对比较复杂的数学模型

把这信息输入进去

用不同的权重

用不同的因果关系

经过一定的计算

当然这个计算别太复杂

至少要在明天开盘之前

你要算出一个结果

这个东西叫什么呢

这个东西叫做向前方的

向未来的一个expectation

一个预计

这个预计你已经司空见惯了

但是现在我们做的这种

backward analysis

是倒过来的

我们如果比喻刚才的那个预计

是一个将来时的话

现在我们有点类似是现在完成时

我们立足于

今天的股票这个市场行情

我们来倒推一下

它之所以演化到今天

在刚刚过去的这一天

它可能发生了一些什么事

平均而言

发生了一些什么事

再举一个简单一些的例子

假设某一个剧场

在这个剧场非常的简化

以至于它只有一排座位

而且它非常有算法

和数据结构的味道

它是只有一端是开口的

另一端是关闭的

OK 现在我们来假设

不同的观众

按照不同的次序来就坐

那么你会发现

越是靠近前端的观众

他入座的成本越低

因为他只要

轻松地坐在那就可以了

反过来 越靠近里端的

越靠近那个盲端的观众

他的入座成本可能会更高

因为在他入座的沿途

如果已经有一些观众在那的话

他们需要起立为他让道

好 如果我们这时候关注

整个这个剧场的入场过程

所需要的时间成本的话

我们确实可以把它分解为

一个观众 一个观众

每个观众入场的成本

而总体的成本

无非就是它们总体的成本之和

那么问题来了

如果这个时候观众已经全部入场了

你来评判一下

在刚刚入场的这个过程中

从期望的意义上讲

从平均的意义上讲

曾经发生过多少成本

如果你是沿着

这样的一个思路来思考

这一类问题的话

那么我们说

它就是一个不折不扣的

backward analysis

后向分析

计算几何课程列表:

00. Introduction

-Before we start

--html

-Evaluation

--html

-Online Judge

--html

-Lecture notes

--html

-Discussion

--html

-A. History of This Course

--00-A. History of This Course

-B. What's Computational Geometry

--00-B. What's Computational Geometry

-B. What's Computational Geometry--作业

-C. How to Learn CG Better

--00-C. How to Learn CG Better

-C. How to Learn CG Better--作业

-D. Why English

--00-D. Why English

01. Convex Hull

-A. Convexity

--01-A-01. Why Convex Hull

--01-A-02. Nails In The Table

--01-A-03. Paint Blending

--01-A-04. Color Space

--01-A-05. Convex Hull

-A. Convexity--作业

-B. Extreme Points

--01-B-01. Extremity

--01-B-02. Strategy

--01-B-03. In-Triangle Test

--01-B-04. To-Left Test

--01-B-05. Determinant

-B. Extreme Points--作业

-C. Extreme Edges

--01-C-01. Definition

--01-C-02. Algorithm

--01-C-03. Demonstration

-C. Extreme Edges--作业

-D. Incremental Construction

--01-D-01. Decrease and Conquer

--01-D-02. In-Convex-Polygon Test

--01-D-03. Why Not Binary Search

--01-D-04. Support-Lines

--01-D-05. Pattern Of Turns

--01-D-06. Exterior/Interior

-D. Incremental Construction--作业

-E. Jarvis March

--01-E-01. Selectionsort

--01-E-02. Strategy

--01-E-03. Coherence

--01-E-04. To-Left Test

--01-E-05. Degeneracy

--01-E-06. Lowest-Then-Leftmost

--01-E-07. Implementation

--01-E-08. Output Sensitivity

-E. Jarvis March--作业

-F. Lower Bound

--01-F-01. Reduction

--01-F-02. CAO Chong's Methodology

--01-F-03. Transitivity

--01-F-04. Reduction: Input

--01-F-05. Reduction: Output

--01-F-06. Sorting ≤_N 2d-CH

-F. Lower Bound--作业

-G. Graham Scan: Algorithm

--01-G-01. Preprocessing

--01-G-02. Scan

--01-G-03. Simplest Cases

-G. Graham Scan: Algorithm--作业

-H. Graham Scan: Example

--01-H-01. Example (1/2)

--01-H-02. Example (2/2)

-H. Graham Scan: Example--作业

-I. Graham Scan: Correctness

--01-I-01. Left Turn

--01-I-02. Right Turn

--01-I-03. Presorting

-I. Graham Scan: Correctness--作业

-J. Graham Scan: Analysis

--01-J-01. Ω(n) Backtracks

--01-J-02. Planarity

--01-J-03. Amortization

--01-J-04. Simplification

-J. Graham Scan: Analysis--作业

-K. Divide-And-Conquer (1)

--01-K-01. Merge

--01-K-02. Common Kernel

--01-K-03. Interior

--01-K-04. Exterior

-K. Divide-And-Conquer (1)--作业

-L. Divide-And-Conquer (2)

--01-L-01. Preprocessing

--01-L-02. Common Tangents

--01-L-03. Topmost + Bottommost ?

--01-L-04. Stitch

--01-L-05. Zig-Zag

--01-L-06. Time Cost

--01-L-07. More Considerations

-L. Divide-And-Conquer (2)--作业

-M. Wrap-Up

--01-M. Wrap-Up

02. Geometric Intersection

-0. Introduction

--02-0. Introduction

-0. Introduction--作业

-A. Preliminary

--02-A-01. EU

--02-A-02. Min-Gap

--02-A-03. Max-Gap

--02-A-04. IEU

-A. Preliminary--作业

-B. Interval Intersection Detection

--02-B-01. Algorithm

--02-B-02. Lower Bound

-B. Interval Intersection Detection--作业

-C. Segment Intersection Reporting

--02-C-01. Brute-force

--02-C-02. Hardness

-C. Segment Intersection Reporting--作业

-D. BO Algorithm: Strategy

--02-D-01. Proximity & Separability

--02-D-02. Comparability & Ordering

--02-D-03. Data Structures

--02-D-04. Possible Cases

-D. BO Algorithm: Strategy--作业

-E. BO Algorithm: Implementation

--02-E-01. Degeneracy

--02-E-02. Event Queue

--02-E-03. Events & Operations

--02-E-04. Sweepline Status

-E. BO Algorithm: Implementation--作业

-F. BO Algorithm: Analysis

--02-F-01. Correctness

--02-F-02. Example

--02-F-03. Retesting

--02-F-04. Complexity of Event Queue

--02-F-05. Complexity of Status Structure

-F. BO Algorithm: Analysis--作业

-G. Convex Polygon Intersection Detection

--02-G-01. Problem Specification

--02-G-02. Monotone Partitioning

--02-G-03. Criterion

--02-G-04. Decrease-And-Conquer

--02-G-05. Example Cases

--02-G-06. Complexity

-G. Convex Polygon Intersection Detection--作业

-H. Edge Chasing

--02-H-01. Eliminating Sickles

--02-H-02. Example

--02-H-03. Analysis

-H. Edge Chasing--作业

-I. Plane Sweeping

--02-I. Plane Sweeping

-I. Plane Sweeping--作业

-J. Halfplane Intersection Construction

--02-J-01. The Problem

--02-J-02. Lower Bound

--02-J-03. Divide-And-Conquer

-J. Halfplane Intersection Construction--作业

03. Triangulation

-0. Methodology

--03-0. Methodology

-0. Methodology--作业

-A. Art Gallery Problem

--03-A-01. Definition

--03-A-02. Lower & Upper Bounds

--03-A-03. Hardness

--03-A-04. Approximation & Classification

-A. Art Gallery Problem--作业

-B. Art Gallery Theorem

--03-B-01. Necessity of floor(n/3)

--03-B-02. Sufficiency by Fan Decomposition

-B. Art Gallery Theorem--作业

-C. Fisk's Proof

--03-C-01. Triangulation

--03-C-02. 3-Coloring

--03-C-03. Domination

--03-C-04. Pigeon-Hole Principle

--03-C-05. Generalization

-C. Fisk's Proof--作业

-D. Orthogonal Polygons

--03-D-01. Necessity of floor(n/4)

--03-D-02. Sufficiency by Convex Quadrilateralization

--03-D-03. Generalization

-D. Orthogonal Polygons--作业

-E. Triangulation

--03-E-01. Existence

--03-E-02. Ear & Mouth

--03-E-03. Two-Ear Theorem

--03-E-04. Well-Order

--03-E-05. Ear Candidate

--03-E-06. Induction

--03-E-07. Well-Order (Again)

--03-E-08. Properties

-E. Triangulation--作业

-F. Triangulating Monotone Polygons

--03-F-01. Monotone Polygon

--03-F-02. Monotonicity Testing

--03-F-03. Strategy

--03-F-04. Stack-Chain Consistency

--03-F-05. Same Side + Reflex

--03-F-06. Same Side + Convex

--03-F-07. Opposite Side

--03-F-08. Example

--03-F-09. Analysis

-F. Triangulating Monotone Polygons--作业

-G. Monotone Decomposition

--03-G-01. Cusps

--03-G-02. Helper

--03-G-03. Helper Candidate

--03-G-04. Sweep-Line Status

--03-G-05. Possible Cases

--03-G-06. Example

--03-G-07. Analysis

-G. Monotone Decomposition--作业

-I. Tetrahedralization

--03-I-01. Polyhedron Decomposition

--03-I-02. Schonhardt's Polyhedron

--03-I-03. Seidel's Polygon

-I. Tetrahedralization--作业

04. Voronoi Diagram

-A. Introduction

--04-A-01. A First Glance

--04-A-02. Dining Halls on Campus

--04-A-03. More Analogies & Applications

--04-A-04. Voronoi

-A. Introduction--作业

-B. Terminologies

--04-B-01. Site & Cell

--04-B-02. Intersecting Halfspaces

--04-B-03. Voronoi Diagram

--04-B-04. Planar Voronoi Diagram

-B. Terminologies--作业

-C. Properties

--04-C-01. Non-Empty Cells

--04-C-02. Empty Disks

--04-C-03. Nearest = Concyclic

--04-C-04. Number of Nearest Sites = Degree

--04-C-05. Split & Merge

-C. Properties--作业

-D. Complexity

--04-D-01. Linearity

--04-D-02. Proof

-D. Complexity--作业

-E. Representation

--04-E-01. Subdivision

--04-E-02. Fary's Theorem

--04-E-03. Representing VD

-E. Representation--作业

-F. DCEL

--04-F-01. Twin Edges

--04-F-02. Half-Edge

--04-F-03. Vertex & Face

--04-F-04. Traversal

--04-F-05. True Or False

--04-F-06. Application

-F. DCEL--作业

-G. Hardness

--04-G-01. 1D Voronoi Diagram

--04-G-02. 2D Voronoi Diagram

--04-G-03. Voronoi Diagram In General Position

-G. Hardness--作业

-H. Sorted Sets

--04-H-01. Convex Hull Made Easier

--04-H-02. Convex Hull As A Combinatorial Structure

--04-H-03. Voronoi Diagram As A Geometric Structure

-H. Sorted Sets--作业

-I. VD_sorted

--04-I-01. ε-Closeness

--04-I-02. Lifting

--04-I-03. Projection

--04-I-04. Case A

--04-I-05. Case B

--04-I-06. Sorting Not Made Easier

-I. VD_sorted--作业

-J. Naive Construction

--J. Naive Construction

-J. Naive Construction--作业

-K. Incremental Construction

--04-K-01. Royal Garden

--04-K-02. Disjoint Union

--04-K-03. Complexity

-K. Incremental Construction--作业

-L. Divide-And-Conquer

--04-L-01. Strategy

--04-L-02. Solving Overlaps

--04-L-03. Contour

--04-L-04. Bisectors

--04-L-05. Y-Monotonicity

--04-L-06. Common Tangents

--04-L-07. Contour Length

--04-L-08. Clip & Stitch

--04-L-09. Intersecting with Cells

--04-L-10. Convexity

--04-L-11. Avoiding Rescans

-L. Divide-And-Conquer--作业

-M. Plane-Sweep

--04-M-01. A First Glance

--04-M-02. Backtracking

--04-M-03. Fortune's Trick

--04-M-04. Frozen Region

--04-M-05. Beach Line

--04-M-06. Lower Envelope

--04-M-07. Break Points

--04-M-08. Events

--04-M-09. Circle Event: What, When & Where

--04-M-10. Circle Event: Why

--04-M-11. Circle Event: How

--04-M-12. Site Event: What

--04-M-13. Site Event: How

-M. Plane-Sweep--作业

05. Delaunay Triangulation

-A. Point Set Triangulation

--05-A-01. Definition

--05-A-02. Edge Flipping

--05-A-03. Upper Bound

--05-A-04. Lower Bound

-A. Point Set Triangulation--作业

-B. Delaunay Triangulation

--05-B-01. Dual Graph

--05-B-02. Triangulation

--05-B-03. Hardness

--05-B-04. History

-B. Delaunay Triangulation--作业

-C. Properties

--05-C-01. Empty Circumcircle

--05-C-02. Empty Circle

--05-C-03. Nearest Neighbor

--05-C-04. Complexity

-C. Properties--作业

-D. Proximity Graph

--05-D-01. Gabriel Graph

--05-D-02. Relative Neighborhood Graph

--05-D-03. Lower Bounds

-D. Proximity Graph--作业

-E. Euclidean Minimum Spanning Tree

--05-E-01. Definition

--05-E-02. Construction

--05-E-03. Subgraph of RNG

--05-E-04. Example

-E. Euclidean Minimum Spanning Tree--作业

-F. Euclidean Traveling Salesman Problem

--05-F-01. Definition

--05-F-02. NP-Hardness

--05-F-03. Approximation

-G. Minimum Weighted Triangulation

--05-G-01. Definition

--05-G-02. Counter-Example

--05-G-03. Hardness

-G. Minimum Weighted Triangulation--作业

-H. Construction

--05-H-01. Subtended Arc

--05-H-02. Angle Vector

--05-H-03. Maximizing The Minimum Angle

--05-H-04. Evolution By Edge Flipping

--05-H-05. Strategies

-H. Construction--作业

-I. RIC With Example

--05-I-01. Idea

--05-I-02. Point Location

--05-I-03. In-Circle Test

--05-I-04. Edge Flipping

--05-I-05. Frontier

--05-I-06. Convergence

-I. RIC With Example--作业

-J. Randomized Incremental Construction

--05-J-01. Recursive Implementation

--05-J-02. Iterative Implementation

--05-J-03. In-Circle Test

--05-J-04. Point Location

-J. Randomized Incremental Construction--作业

-K. RIC Analysis

--05-K-01. Time Cost

--05-K-02. Backward Analysis

--05-K-03. Preconditions

--05-K-04. Types Of Edge Change

--05-K-05. Number Of Edge Changes

--05-K-06. Average Degree

--05-K-07. Number Of Rebucketings

--05-K-08. Probability For Rebucketing

--05-K-09. Expectation

--05-K-10. Further Consideration

06. Point Location

-0. Online/Offline Algorithms

--06-0. Online/Offline Algorithms

-0. Online/Offline Algorithms--作业

-A. Introduction

--06-A-01. Where Am I

--06-A-02. Point Location

--06-A-03. Assumptions For Clarity

--06-A-04. Input Size

--06-A-05. Performance Measurements

--06-A-06. A Global View

-A. Introduction--作业

-B. Slab Method

--06-B-01. Slab Decomposition

--06-B-02. Ordering Trapezoids

--06-B-03. Tree of Trees

--06-B-04. Example

--06-B-05. Query Time

--06-B-06. Preprocessing Time

--06-B-07. Storage Cost

--06-B-08. Worst Case

-B. Slab Method--作业

-C. Persistence

--06-C-01. Ephemeral Structure

--06-C-02. Persistent Structure

--06-C-03. Persistent Slabs

-C. Persistence--作业

-D. Path Copying

--06-D-01. Strategy

--06-D-02. X-Search

--06-D-03. Storage Optimization

-D. Path Copying--作业

-E. Node Copying

--06-E-01. O(1) Rotation

--06-E-02. Strategy

--06-E-03. Why Red-Black

--06-E-04. Linear Space

--06-E-05. Time Penalty

-E. Node Copying--作业

-F. Limited Node Copying

--06-F-01. Idea

--06-F-02. Split

--06-F-03. Complexity

--06-F-04. Recoloring

-G. Kirkpatrick Structure

--06-G-01. Optimal And Simpler

--06-G-02. Triangulation

--06-G-03. Example

--06-G-04. Hierarchy

--06-G-05. Independent Subset

--06-G-06. The More The Better

--06-G-07. The Fewer The Better

--06-G-08. Degree

--06-G-09. Existence Of Independent Subset

--06-G-10. Construction Of Independent Subset

--06-G-11. DAG

-G. Kirkpatrick Structure--作业

-H. Trapezoidal Map

--06-H-01. Ray Shooting

--06-H-02. Decomposition

--06-H-03. Properties & Complexity

--06-H-04. Search Structure: Example

--06-H-05. Search Structure: Nodes

--06-H-06. Search Structure: Performance

-H. Trapezoidal Map--作业

-I. Constructing Trapezoidal Map

--06-I-01. Initialization

--06-I-02. Iteration

--06-I-03. Challenges

--06-I-04. Case 1: Two Endpoints

--06-I-05. Case 2: One Endpoint

--06-I-06. Case 3: No Endpoints

--06-I-07. Example

-J. Performance Of Trapezoidal Map

--06-J-01. Randomization

--06-J-02. Expectation

--06-J-03. Number Of Ray Trimmed

--06-J-04. Number Of Trapezoidals Created (1)

--06-J-05. Number Of Trapezoidals Created (2)

--06-J-06. Time For Point Location

--06-J-07. Size Of Search Structure

--06-J-08. Fixed Query Point + Randomly Created Maps

--06-J-09. Each Single Step

--06-J-10. Probability Of Enclosing Trapezoid Changed

--06-J-11. Query Time

07. Geometric Range Search

-A. Range Query

--07-A-01. 1-Dimensional Range Query

--07-A-02. Brute-force

--07-A-03. Binary Search

--07-A-04. Output Sensitivity

--07-A-05. Planar Range Query

-A. Range Query--作业

-B. BBST

--07-B-01. Structure

--07-B-02. Lowest Common Ancestor

--07-B-03. Query Algorithm

--07-B-04. Complexity (1)

--07-B-05. Complexity (2)

-B. BBST--作业

-C. kd-Tree: Structure

--07-C-01. 2d-Tree

--07-C-02. Example

--07-C-03. Construction

--07-C-04. Example

--07-C-05. Canonical Subsets

-C. kd-Tree: Structure--作业

-D. kd-Tree: Algorithm

--07-D-01. Query

--07-D-02. Example

--07-D-03. Optimization

-D. kd-Tree: Algorithm--作业

-E. kd-Tree: Performance

--07-E-01. Preprocessing Time + Storage

--07-E-02. Query Time

--07-E-03. Beyond 2D

-E. kd-Tree: Performance--作业

-F. Range Tree: Structure

--07-F-01. x-Query + y-Query

--07-F-02. Worst Case

--07-F-03. x-Query * y-Queries

-F. Range Tree: Structure--作业

-G. Range Tree: Query

--07-G-01. Painters' Strategy

--07-G-02. X-Tree

--07-G-03. Y-Trees

--07-G-04. Algorithm

-G. Range Tree: Query--作业

-H. Range Tree: Performance

--07-H-01. Storage

--07-H-02. Preprocessing Time

--07-H-03. Query Time

--07-H-04. Beyond 2D

-H. Range Tree: Performance--作业

-I. Range Tree: Optimization

--07-I-01. Y-Lists

--07-I-02. Coherence

--07-I-03. Idea

--07-I-04. Fractional Cascading

--07-I-05. Complexity

08. Windowing Query

-A. Orthogonal Windowing Query

--08-A-01. Definition

--08-A-02. Classification

-A. Orthogonal Windowing Query--作业

-B. Stabbing Query

--08-B-01. 1D Windowing Query

--08-B-02. Stabbing Query

-C. Interval Tree: Construction

--08-C-01. Median

--08-C-02. Partitioning

--08-C-03. Balance

--08-C-04. Associative Lists

--08-C-05. Complexity

-C. Interval Tree: Construction--作业

-D. Interval Tree: Query

--08-D-01. Algorithm (1)

--08-D-02. Algorithm (2)

--08-D-03. Complexity

-D. Interval Tree: Query--作业

-E. Stabbing With A Segment

--08-E-01. Definition

--08-E-02. Interval Tree

--08-E-03. Query Algorithm (1)

--08-E-04. Query Algorithm (2)

--08-E-05. Overview

--08-E-06. Complexity

-F. Grounded Range Query

--08-F-01. O(n) Space

--08-F-02. 2D-GRQ

--08-F-03. 1D-GRQ Using Range Tree

--08-F-04. 1D-GRQ By Linear Scan

-G. 1D-GRQ Using Heap

--08-G-01. Heap

--08-G-02. Query

--08-G-03. Example

--08-G-04. Complexity

-G. 1D-GRQ Using Heap--作业

-H. Priority Search Tree

--08-H-01. PST = Heap + BBST

--08-H-02. Order Property

--08-H-03. Sibling Partitioning

--08-H-04. Construction

-H. Priority Search Tree--作业

-I. 2D-GRQ Using PST

--08-I-01. Algorithm (1/2)

--08-I-02. Algorithm (2/2)

--08-I-03. Example (1/3)

--08-I-04. Example (2/3)

--08-I-05. Example (3/3)

--08-I-06. Query Time (1/3)

--08-I-07. Query Time (2/3)

--08-I-08. Query Time (3/3)

-I. 2D-GRQ Using PST--作业

-J. Segment Tree

--08-J-01. General Windowing Query

--08-J-02. Elementary Interval

--08-J-03. Discretization

--08-J-04. Worst Case

--08-J-05. BBST

--08-J-06. Solving Stabbing Query

--08-J-07. Worst Case

--08-J-08. Common Ancestor

--08-J-09. Canonical Subsets

--08-J-10. O(nlogn) Space

--08-J-11. Constructing A Segment Tree

--08-J-12. Inserting A Segment (1)

--08-J-13. Inserting A Segment (2)

--08-J-14. Inserting A Segment (3)

--08-J-15. Query Algorithm

--08-J-16. Query Time

-K. Vertical Segment Stabbing Query

--08-K-01. Review

--08-K-02. X-Segment Tree

--08-K-03. Associative Structure

--08-K-04. Vertical Segment Stabbing Query

05-K-02. Backward Analysis笔记与讨论

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