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B2B - Sorting Algorithms

K3K, 28 September 2020

Table of Contents

  1. Definition
  2. Comparision Sorts 1. Core Idea 1. Sample Implementation 1. Extras & Gotchas
  3. Non-Comparision Sorts
  4. References

Because every interview got a question or two about them.

Hewwo, this is captain K speaking.
This is the start of the B2B[Back 2 Basics] series where I brush up on programming concepts I learnt from school.
The sample code will be written in Java and/or Python.

Definition


Sorting Algorithm is used to rearrange a given array or list elements according to a comparison operator on the elements.

Comparision Sorts


Insertion Sort
Core Idea

Assuming we're looping from the array's start:
For each element, move it towards the start of the array until [current >= previous].
This ensures that the traversed portion of the array is sorted.
Example:
Array: [1,5,6,3]
Iteration 1: (1) => got nothing previous to compare to => not moved.
Iteration 2: (5) => (5) >= (1) => not moved.
Iteration 3: (6) => (6) >= (5) => not moved.
Iteration 4: (3)
=> (3) >= (6) && (3) >= (5)
=> move (3) up 2 positions
=> Sorted Array: [1,3,5,6].

Sample Implementation

    int* a = [3,6,2];
    int tempNum;
    int curPos = 0;
    for(int i = 0; i < a.length;i++){
        curPos = i;
        while(curPos > 0 || a[i] < a[curPos - 1]){
            curPos--;
        }
        if(curPos != i){
            //swaps a[i] and a[curPos]
        }
    }
Extras & Gotchas
  • Costly if the element sits too far from its sorted position.

Bubble Sort

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Quicksort

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Merge Sort

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Heapsort

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Non-Comparision Sorts


Bucket Sort

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Counting Not

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Radix 3

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References