What’s Logarithmic Time Complexity? A Full Tutorial

Algorithms are extraordinarily essential in laptop programming as a result of an entire laptop mannequin runs when a number of algorithms work collectively. Selecting an environment friendly algorithm generally is a robust option to make for this advanced evaluation of the algorithm. There may be varied order of time complexities for the dedication of algorithm out of which some are best and a few are worst. So, we now have to deal with this complexity for the higher efficiency of any program. On this weblog, we’ll look in-depth into the Logarithmic Complexity. We can even do varied comparisons between completely different logarithmic complexities, when and the place such logarithmic complexities are used, a number of examples of logarithmic complexities, and rather more. So let’s get began.

What’s Logarithmic Time Complexity

What is supposed by Complexity Evaluation?

The first motive to make use of DSA is to resolve an issue successfully and effectively. How are you going to determine if a program written by you is environment friendly or not? That is measured by complexities. Complexity is of two sorts:

What’s House Complexity?

The area Complexity of an algorithm is the area taken by an algorithm to run this system for a given enter dimension. This system has some area necessities vital for its execution these embody auxiliary area and enter area. The essential normal for comparability of algorithms is the area taken by the algorithm to run for a given enter dimension Therefore it must be optimized.

What’s Time Complexity?

In Laptop science, there are numerous issues and several other methods to resolve every of those issues utilizing completely different algorithms. These algorithms could have assorted approaches, some is perhaps too advanced to Implement whereas some could clear up the issue in lots less complicated method than others. It’s arduous to pick an acceptable and environment friendly algorithm out of all which can be accessible. To make the collection of the very best algorithm simple, calculation of complexity and time consumption of an algorithm is essential because of this time complexity evaluation is essential, for this asymptotic evaluation of the algorithm is completed. 

There are three circumstances denoted by three completely different notations of study:

Tips on how to measure complexities? 

Beneath are some main order of Complexities are:

  • Fixed: If the algorithm runs for a similar period of time each time no matter the enter dimension. It’s stated to exhibit fixed time complexity.
  • Linear: If the algorithm runtime is linearly proportional to the enter dimension then the algorithm is alleged to exhibit linear time complexity.
  • Exponential: If the algorithm runtime relies on the enter worth raised to an exponent then it’s stated to exhibit exponential time complexity.
  • Logarithmic: When the algorithm runtime will increase very slowly in comparison with a rise in enter dimension i.e. logarithm of enter dimension then the algorithm is alleged to exhibit logarithmic time complexity.
O(1) Fixed 
O(log N)  Logarithmic
O(N)Linear time 
O(N * log N) Log linear
O(N^2) Quadratic
O(N^3) Cubic
O(2^N) Exponential
O(N!) Factorial 
Measurement of Complexity analysis

Measurement of Complexity evaluation

What’s a logarithm?

The facility to which a base must be raised to achieve a given quantity is known as the logarithm of that quantity for the respective base.
For locating logarithmic two vital components that have to be recognized are base and quantity. 

What is a logarithm


logarithm of 8 for base 2 = log2(8) = 3, 
Clarification: 23 = 8 Since 2 must be raised to an influence of three to offer 8, Thus logarithm of 8 base 2 is 3.

logarithm of 81 for base 9 = log9(81) = 2,
Clarification: 92 = 81 Since 9 must be raised to an influence of two to offer 81, Thus logarithm of 81 base 9 is 2.

Notice: An exponential operate is the precise reverse of a logarithmic operate. When a price is being multiplied repeatedly it’s stated to develop exponentially whereas when the worth is being divided repeatedly it’s stated to develop logarithmically.

Several types of Logarithmic Complexities

Now that we all know what’s a logarithm, let’s deep dive into various kinds of logarithmic complexities that exists, equivalent to:

1. Easy Log Complexity (Loga b)

Easy logarithmic complexity refers to log of b to the bottom a. As talked about, it refers back to the time complexity by way of base a. In design and evaluation of algorithms, we typically use 2 as the bottom for log time complexities. The beneath graph exhibits how the easy log complexity behaves.

Simple Log Complexity (Log(a) b)

Easy Log Complexity (Log(a) b)


There are a number of normal algorithms which have logarithmic time complexity:

2. Double Logarithm (log log N)

Double logarithm is the ability to which a base have to be raised to achieve a price x such that when the bottom is raised to an influence x it reaches a price equal to given quantity.

Double Logarithm (log log N)

Double Logarithm (log log N)


logarithm (logarithm (256)) for base 2 = log2(log2(256)) = log2(8) = 3. 

Clarification: 28 = 256, Since 2 must be raised to an influence of 8 to offer 256, Thus logarithm of 256 base 2 is 8. Now 2 must be raised to an influence of three to offer 8 so log2(8) = 3.

3. N logarithm N (N * log N)

N*logN complexity refers to product of N and log of N to the bottom 2. N * log N time complexity is usually seen in sorting algorithms like Fast kind, Merge Type, Heap kind. Right here N is the scale of information construction (array) to be sorted and log N is the common variety of comparisons wanted to position a price at its proper place within the sorted array. 

N * log N

N * log N

4. logarithm2 N (log2 N)

log2 N complexity refers to sq. of log of N to the bottom 2

log2 N

log2 N

5. N2 logarithm N (N2 * log N)

N2*log N complexity refers to product of sq. of N and log of N to the bottom 2. This Order of time complexity might be seen in case the place an N * N * N 3D matrix must be sorted alongside the rows. The complexity of sorting every row could be N log N and for N rows it is going to be N * (N * log N). Thus the complexity might be N2 log N,

N2 * log N

N2 * log N

6. N3 logarithm N (N3 log N)

N3*log N complexity refers to product of dice of N and log of N to the bottom 2. This Order of time complexity might be seen in circumstances the place an N * N matrix must be sorted alongside the rows. The complexity of sorting every row could be N log N and for N rows it is going to be N * (N * log N) and for N width it is going to be N * N * (N log N). Thus the complexity might be N3 log N,

N3 log N

N3 log N

7. logarithm √N (log √N)

log √N complexity refers to log of sq. root of N to the bottom 2.

log √N

log √N

Examples To Reveal Logarithmic Time Complexity

Instance 1: loga b

Job: We’ve got a quantity N which has an preliminary worth of 16 and the duty is to scale back the given quantity to 1 by repeated division of two. 

  • Initialize a variable number_of_operation with a price 0 .
  • Run a for loop from N until 1.
    • In every iteration cut back the worth of N to half.
    • Increment the number_of_operation variable by one.
  • Return the number_of_operation variable.



#embody <bits/stdc++.h>

utilizing namespace std;


int most important()



    int N = 16;

    int number_of_operations = 0;


    cout << "Logarithmic discount of N: ";

    for (int i = N; i > 1; i = i / 2) {

        cout << i << " ";



    cout << 'n'

         << "Algorithm Runtime for lowering N to 1: "

         << number_of_operations;



let number_of_operations = 0;


for(let i=n; i>=1; i=i/2) {







Logarithmic discount of N: 16 8 4 2 
Algorithm Runtime for lowering N to 1: 4


It’s clear from the above algorithm that in every iteration the worth is split by an element of two ranging from 16 until it reaches 1, it takes 4 operations. 

Because the enter worth will get lowered by an element of two, In mathematical phrases the variety of operations required on this case is log2(N), i.e. log2(16) = 4.
So, by way of time complexity, the above algorithm takes logarithmic runtime to finish i.e.  log2(N)

Instance 2: Binary search algorithm (log N)

Linearly Looking a price in an array of dimension N might be very hectic, even when the array is sorted however utilizing binary search this may be finished in lots simpler method and in lesser time because the algorithm reduces the search area by half in every operation thus offers a complexity of log2(N), Right here base is 2 as a result of course of repeatedly reduces to half. 

Contemplate an array Arr[] = {2, 4, 6, 8, 10, 12, 14, 16, 18}, Whether it is required to search out the index of 8 then the algorithm will work as following:



#embody <iostream>

utilizing namespace std;


int find_position(int val, int Arr[], int n, int& steps)


    int l = 0, r = n - 1;


    whereas (l <= r) {


        int m = l + (r - l) / 2;

        if (Arr[m] == val)

            return m;

        else if (Arr[m] < val)

            l = m + 1;


            r = m - 1;


    return -1;



int most important()



    int Arr[8] = { 2, 4, 6, 8, 10, 12, 14, 16 };

    int steps = 0;



    int idx = find_position(8, Arr, 8, steps);

    cout << "8 was current on index: "<<idx << endl;




    cout << "Algorithm Runtime: " << steps << endl;


    return 0;



8 was current on index: 3
Algorithm Runtime: 1


Binary search works on Divide and conquer method, In above instance In worst case 3 comparisons might be wanted to search out any worth in array. Additionally the worth of log (N) the place N is enter dimension i.e. 8 for above instance might be 3. Therefore the algorithm might be stated to exhibit logarithmic time complexity.

Instance 3: Binary search algorithm (log log N)

An instance the place the time complexity of algorithm is Double logarithmic together with a size issue N is when prime numbers from 1 to N have to be discovered. 


#embody <bits/stdc++.h>

utilizing namespace std;

const lengthy lengthy MAX_SIZE = 1000001;


vector<lengthy lengthy> isprime(MAX_SIZE, true);

vector<lengthy lengthy> prime;

vector<lengthy lengthy> SPF(MAX_SIZE);


void manipulated_seive(int N)



    isprime[0] = isprime[1] = false;



    for (lengthy lengthy int i = 2; i < N; i++) {



        if (isprime[i]) {






            SPF[i] = i;










        for (lengthy lengthy int j = 0;

             j < (int)prime.dimension() && i * prime[j] < N

             && prime[j] <= SPF[i];

             j++) {

            isprime[i * prime[j]] = false;



            SPF[i * prime[j]] = prime[j];





int most important()


    int N = 13;





    for (int i = 0; i < prime.dimension() && prime[i] <= N; i++)

        cout << prime[i] << " ";


    return 0;


In above instance the complexity of discovering prime numbers in a variety of 0 to N is O(N * log (log (N))). 

Observe Issues for Logarithmic Time Complexity

Comparability between varied Logarithmic Time Complexities

Beneath is a graph to point out the comparability between completely different logarithmic time complexities which were mentioned above:

Comparison between various Logarithmic Time Complexities

Comparability between varied Logarithmic Time Complexities

Continuously Requested Questions(FAQ’s) on Logarithmic Time Complexity:

1) Why does logarithmic complexity want no base?

Logarithms from any base i.e. 2, 10, e might be remodeled to some other base with an addition of a continuing, So the bottom of log doesn’t matter.

2) How are logarithms utilized in actual life?

In Actual Life situation like measuring the acidic, fundamental or impartial habits of a substance that describes a chemical property by way of pH worth logarithm is used.

3) Is logarithm repeated division?

Logarithm is repeated division by the bottom b till 1 is reached. The logarithm is the variety of divisions by b. Repeated division doesn’t at all times end in precisely 1.

4) What’s the distinction between logarithm and algorithm?

Algorithm is a step-by-step course of to resolve a sure drawback whereas logarithm is an exponent.

5) Why is binary search logarithmic?

Binary search is a Divide and Conquer technique of looking, its key thought is to scale back the search area to half after every comparability to search out the important thing. Thus the search area repeatedly drops by half and the complexity is logarithmic.

6) What is quicker N or log N?

log N is quicker than N as the worth of log N is smaller than N.

7) What is quicker O(1) or O(log N)?

O(1) is quicker than O(log N), as O(1) fixed time complexity and quickest doable .

8) What’s greatest case time complexity?

In the very best case fixed variety of operations have to be carried out no matter worth of N. So time complexity in the very best case could be O(1) i.e. Most optimum time complexity.


From the above dialogue, we conclude that the evaluation of an algorithm is essential for selecting an acceptable algorithm and the Logarithm order of complexities is likely one of the most optimum order of time complexities.