Books and Articles Snippets 😎🧑🏻‍✈️

📒 From Quora: 

• Some people are happy with a low key life. Happiness is the great equalizer. If they are happy, your expectations no longer matter.

 

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Interrupt Behavior || ARM Cortex

Interrupt Behavior:-
-----------------------------

Interrupt/Exception Sequence:-
------------------------------------------
when an exception takes place:
1- Stacking: push 8 registers' content to stack
2- Vector Fetch: reading the exception handler starting address from the vector table (IVT).
3- Update of Stack Pointer, Linker Register (LR) and Program Counter (PC).

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Data Structure

Data Structure main topics:
----------------------------------
Linked List
Stack
Queue
Tree
--------------------------------------------------------------------------------------------------------
Array: is the best data structure in terms of accessing time as the time complexity of it is O(1) the time required to access any element of it is constant. Problem: Memory usage!

Linked List: 
is the best data structure in terms of memory management but in terms of accessing time is O(N). Problem: Accessing time- Time complexity is O(N)!

Types:
          - Simply Linked List.
          - Doubly Linked List.

-------------------------------------------------------------------
Key Word to implement linked list is to draw it.
--------------------------------------------------------------------
Note:
Each node in the linked list should be similar to all o them. As the struct (Node) is considered as a user-defined data type so each structure is a data type defined by the number and the type of its members. So we can not change the node structure as that means change the type of the pointer used within the node to point to the next node and the previous one.



=======================================================
Stack (Last In First Out (LIFO)):
--------------------------------------------
* Push in Stack
             - Before pushing data we should make sure the stack is not full.
*Pop from Stack
             - Before popping from the stack we should make sure that the stack is not empty.

Stack use case:-
---------------------
We can mirror a string by pushing it in a stack then popping it again.

3 Elements For the Stack:
----------------------------------
- Pointer to the Top of Stack (TOS)
- Store Stack Size
- Store Data in Stack

So we need to implement Stack as :

typedef struct stack
{
       int *stkTos; /*Pointer to the top of the Stack*/
       int tos;  /**/
      int size;  /**/
}stack;

________________________________________________________________________

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Sorting Algorithms

Sorting Algorithms:
---------------------------
1- Selection Sort
2- Bubble Sort
3- Merge Sort
============================================================
1- Selection Sort: 
- Time Complexity : O(N^2)
---------------------------------------
void swap(int*ele1,int*ele2)
{
int temp;
temp=*ele1;
*ele1=*ele2;
*ele2=temp;
}

/*
in this code: the use of mini variable is to determine the index of the smallest number in the array first then we swap after the inner loop finishes. Without the mini variable, we have to move the swap function into the inner loop and swap whenever the condition is true and that takes more time!
*/
void selectSortElements(int*arr,int size)
{
int i,j,mini;
for(i=0;i<size-1;i++)
{

mini=i;

/* The inner for loop is used to determine the index of the smallest element in the array */
for(j=i+1;j<size;j++)
{
if(arr[j]<arr[mini])
{
mini=j;
}
}
swap(&arr[i],&arr[mini]);
}
}

=================================================
2-Bubble Sort:-
--------------------

void bubbleSort(int*arr , int size)
{
    int i,j;

    for(i=0;i<size-1;i++)
    {
        for(j=0;j<size-i-1;j++)
        {
            if( arr[j]>arr[j+1])
            {
                 swap(&arr[j],&arr[j+1]);
             }   
         }
    }
}

The above function always runs O(n^2) time even if the array is sorted.It can be optimized by stopping the algorithm if inner loop didn’t cause any swap.

The optimized version of bubble sort:
---------------------------------------------------

void bubbleSort(int*arr, int size)
{
int i , sortFlag=0;
while(!sortFlag)
{
sortFlag=1;
for(i=size-1;i>=0;i--)
{
if(arr[i]<arr[i-1])
{
swap(&arr[i],&arr[i-1]);
sortFlag=0;
}
}
}
}

NOTES:
========

Worst and Average Case Time Complexity: O(n*n). Worst case occurs when array is reverse sorted.

Best Case Time Complexity: O(n). Best case occurs when array is already sorted.

=========================================================
Merge Sort:
------------------

Perfectly explained: https://www.geeksforgeeks.org/merge-sort/

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Searching Algorithm

Searching Algorithms:
---------------------------
1-Sequential Search
2- Binary Search
----------------------------------------------------------
1- Sequential Search:
    -Searching in an array of N.
    -Time complexity: O(N)

int sequentialSearch (int * arr, int size, int data)
{
       int index= -1;
       int i;
       for(i=0;i<size;i++)
       {
          if(arr[i] == data)
          {
           return i; /* Once the data is found return the index and exit the function*/
           }
         }
       return index;
}

===================================================================
2- Binary Search: is applied on "Sorted data" 
    - Data must be sorted.
    - Time Complexity: O(log N)

int binarySearch(int*arr, int size ; int data)
{
int low=0;
int high=size-1;
while(low<=high)
{
mid=(low+high)/2;
if(data>arr[mid])
{
low=mid+1
}
else if(data<arr[mid])
{
high=mid-1;
}
else
{
return mid;
}
return -1;
}

---------------------------------------------------
The same Function using Recursion:

int recBinarySearch(int*arr,int low , int high,int data)
{
int mid=(high+low)/2;
if(low>highh)
{
return -1;
}
if(arr[mid] < data)
{
  low=mid+1;
return recBinarySearch(arr,low,high,data);
}
else if (arr[mid] > data)
{
  high=mid-1;
return recBinarySearch(arr,low,high,data);
}
else
return mid;
}
============================================================

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Matrices (mathematics)

Matrices Addition and Subtraction:-
=============================
************************************************************************
Rule:
You can only Add or subtract two matrices only and only if they have the same number of rows and columns and the result will have the same number of rows and columns.

***************************************************************************
Addition or subtraction is performed between the two elements that have the same location.

Ex:

[ 5      4              [ 9      -3               [ (9+5)    (4-3)                  [14       1
   -1    6         +     8      2         =       (-1+8)   (6+2)          =        7         8
    0     7 ]               -6    1 ]                (0-6)      (7+1) ]                -6          8 ]

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