(BST是锻炼递归代码的好题目)

1. Binary Search Trees

def. BST
A binary tree where each node has a key:
for every node, the key is larger than all nodes in left subtree, smaller than all nodes in right subtree.

Fields: key, val, left, right

Implementation

An inner class of BST nodes:

private class …

1. Symbol Table API

key-value pair abstraction

• insert a value with a key
• given a key, search for its value

Association array abstraction

Associate a value to a key — generalized array: a[key]=val.

public class ST<Key, Value>{   
    void put(Key k, Value v);//remove key if value=null …

1. API and elementary implementations

Collection: data struct for inserting and deleting items (ex. stack and queue).
Priority queue: a special kind of collection — remove largest/smallest element.

API:

public class Max<Kye implements Comparable<Key>>{   
    public MaxPQ();    
    public void insert(Key k);   
    public Key delMax();    
    public boolean isEmpty();     
    public …

(maybe best algorithm for sorting.)

1. Quicksort

Idea:

1. shuffle the array
2. Partition the array into two subarrays to left and right of pivot (now pivot is in its final position)

no larger entry to the left of pivot
no smaller entry to the right of pivot

1. sort each subarray recursively …

Two classical sorting algorithms: mergesort, quicksort.

1. Mergesort

Divide and conquer: top 10 algorithms of the 20th century, invented by von Neumann.

Idea:

• divide array into 2 halves
• recursively sort each half
• merge two sorted halves

Implementation

Merge:
Goal: a[lo] to a[mid] and a[mid+1] to a …

1. Introduction

rearanging array of size N into ascending order
test client code: Insertion.sort(a);

sort any datatype

callback

callback = reference to executable code
i.e. passing functions as argument to sort() method
sort() function calls object's compareTo() method

→ implement the Comparable interface:

    public class XX implements Comparable<XX …

fundamental data types: stacks and queues operations: insert, remove, test empy, iterate,...

module programming: seperate interface and implementation

1. Stacks

ex. a stack of strings

• API:

  public interface StackoOfStrings{ void push(String item); String pop(); boolean isEmpty(); //int size(); }

implementation 1: using a linkedlist

insert/remove from the top of …

model & problem

(原文描述太啰嗦了)
A system using an N-by-N grid of sites.
→ Each site is either open or blocked.
→ A full site is an open site that can be connected to an open site in the top row via a chain of neighboring open …

1. Introduction

2. Observations

ex. 3-SUM pb
given N distinct numbers, how many triples sum up to 0? (pb related to computatioal geogtry)

• brute force method:

for(int i=0;i<N;i++)
    for(int j=i+1;j<N;j++)
        for(int k=j+1;k<N;k++)
            {if …

Part 0: Preliminaries

Each line in the ratings dataset (ratings.dat.gz) is formatted as:
UserID::MovieID::Rating::Timestamp ⇒ tuples of (UserID, MovieID, Rating)in ratingsRDD
Each line in the movies (movies.dat) dataset is formatted as:
MovieID::Title::Genres ⇒ tuples of (MovieID, Title) in ratingsRDD

487650 ratings and 3883 …