Binary Search Tree Structure and algorithm

2018-05-04

Traversals

Preorder Traversal, Process(Root), GotoLeft, GotoRight

process(root);

preOrder(leftSubtree);

preOrder(rightSubtree);

InOrder, GotoLeft, Process, GotoRight
1
// This will get a ordered list

PosrOrder, Left, Right, Process

1
2
3

// If we put operators to root, and number to lefts,

// then this order will match postFix (expression)

And these 3 different orders can match the prefix, infix, postfix expressions.

Docker Commands Cheatsheet

2018-05-04

docker start

   docker run

   docker stop

   docker exec -it container_name bash //run commands in container

   docker rm // remove container

   docker rmi // remove image

   docker images -a // list all images

   docker container ls //list all container

refs

Data Warehouse Data Quality

2018-05-01

Issues in source data

out of acceptable range
non-standard data/ varying formats
outliers, outliers is above/below 3* standard deviation
invalid values
null values
differing culture rules (like, nz/us time date format)
cosmetic
verification (wrong post code)

strategy

filter/clean/correct errors in source date before transform
quality assured by verifying again
correct and complete
pre-processing

Data Quality(DQ) Assurance process

checking
- checking if there is an error or dirty data
- based on pre-defined data quality rules
Logging
- record the data with errors
- notify DB users/admin to correct the data
Correcting
- clean or ignore the erros in the data – data cleaning

Logging errors

DQ rule is violated, log the event into a table. (the below is the fields of the table)

RowID of the record that vialoates the rule a physical address the row stored on disk
rule no that is violated
table name of that row id
Database name of the table
Action -> Reject/Allow/Fix

DQ Actions

Reject
Allow (low risk error, the error is in within tolerance limits)
Fix (Correct the error)

Reading

sql server trigger

Week7 Android Google Api And Polyline

2018-04-30

fragmentactivity can be used to design better UI

Google map

polyline to generate polygen
marker (google map)
GroundOverlayOptions (google map add ground overlay)
addcircle
setonPolylineClickListener
moveCamera
use emulator with google api

Refs

google map api document

Data Structure, Linked list

2018-04-11

Linked list

We only need a single pointer to identify the list, however, it is a good idea to have a node containing data about a list, this data is metadata.

Addignment requirements

full list, try catch no memorary exeption

Thread on Android

2018-04-09

Thread thread = new Thread()
{
public void run()
    { //some codes here
    }
};
thread.run()

Some mistakes learners made

thread.start(), not use run directly
reading from different thread is OK, writing might be a problem

Some tips

threads that have dead cannot be restarted
lot of problmes of reading/writing

Race conditions

execution of threads is not-deterministic
executation order effects outcome
program may run correctly 99.99%ek5
no problem if you are just reading shared data

synchronized

only one thread can access this object or the execute this section of code one time
other threads will wait
can solve non-deterministic issues during runiing

Dead lock

two or more threads are locked forever - waiting to acquire locks to shared objects that each thread has a lock against
a circular dependacy between threads and locks

Asp.net Core data migration

2018-03-19

how do we start

database / data model
class (null if you already get data model)
code

data model

when you define a property name like <name>Id, Entity Framework treat it as a key
or use fluent api to define
fluent api get better perfomance

data migration

change userid in connecting string to user
you create multi migrations before update it

Mobile android class notes

2018-03-12

generate shotcut

cmd+n
cmd+shift+n

constraints

blue button

Log

invalidate

force to redraw, if you call it in onDraw(), it will be called again and again, like a loop.

package uno.bai.tim.test;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;

/**
 * Created by tim on 12/03/18.
 */

public class EasyView extends View {

    float x =50;
    float y =50;



    public EasyView(Context context) {
        super(context);
    }

    public EasyView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
    }

    public EasyView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }


    @Override
    protected void onDraw(Canvas canvas) {

        Paint paint = new Paint();
        paint.setColor(Color.LTGRAY);

        canvas.drawCircle(x,y,20,paint);
        x++;
        y++;

        invalidate(); 
//        


//        super.onDraw(canvas);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        return super.onTouchEvent(event);
    }
}