jas0nhuang

Don't LeetCode Yet - 1&2 - Think First

Think Before You Code

Think about the processes thoroughly, organize and write down Flowchart (execution steps) and/or Pseudocode before actually coding.

One process each line. Expression, Condition, Repetition.

Some Examples

Let theNumber equals to 1
    1. If theNumber larger then 100
        -> Stop the program
    2. If theNumber smaller then 100 
        -> If theNumber is even
            -> Print out theNumber
        -> If theNumber is odd
            -> Do nothing
        -> Add 1 to theNumber 
        -> Go back to 1.

pseudocode:

1 let theNumber = 1
2    if theNumber > 100
3        exit
4    else
5        if theNumber % 2 === 0
6            print theNumber
7    theNumber = theNumber + 1
8    back to line 2

also:

for theNumber from 1 to 100
    if theNumber % 2 === 0
        print theNumber

Indent each section in the code makes the code more readable. Like the for, if and print section above.

Fizz Buzz

Print fizz if the number is multiple of 3, print buzz if the number is multiple of 5, and print fizzbuzz if the number is multiple of 3 and 5.
Some brute force solutions and some BETTER solutions (String Concatenation, Hash).

Find the smallest card

let smallCard = firstCard
for i from 1 to N
    if card i < smallCard
        smallCard = card i

Project 1

  1. Reverse String

    let outputStr = ""
    for i from stringLength to 0
        outputStr += originalStr[i]
    print outputStr

  2. Array sum

    let result = 0
    for i from 1 to array length
        result += array[i]
    print the result

  3. Find the biggest

    let the bigCard = the firstCard
    for i from 1 to total cards number
        if card i > bigCard
            bigCard = card i

Computational Thinking

Think one step at a time. Read a piece of code and try to execute the code line by line in your head.

Useful tips for reading the code

Use Chrome Devtool Debugger

Just add the word debugger in the beginning of the JavaScript code.
For Firefox Devtool. Need to set a break point by clicking on the line number at the left of the code.
These Devtools can run the code step by step

Console.log everything

When console.log out an array, we can STRINGIFY (JSON.stringify()) it to show the actual content at that moment (but not the one that has been modified latter).

Examples

  1. Find second large

    let max = -Infinity 
        //but not array[0].
        // Or else there will be some problem finding solution.
    let max2 = -Infinity

  2. Lower case string to Upper case
    Some knowledge about ASCII code
    ASCII code:
    a: 97 z:122 A:65 Z:90 (add 32 to exchange Upper case to lower case.)
    Function in JavaScript
    "a".charCodeAt(0) will give the ASCII code for “a”
    String.fromCharCode("a".charCodeAt(0) - 32) this will get the character “A”
    s.toUpperCase() shortcut!

  3. Delete a certain character

Project 2

Observe the structure of the code.
Write down the execution step by step by reading the code.

  1. Find Second max
  2. Lower Upper case exchange
  3. Find the divisor of a number
    Em…here are the solutions:ALG101-too-weak-to-leetcode/unit2