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Definition, Types, Complexity and Examples of Algorithm

Last Updated : 16 Oct, 2023
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An algorithm is a well-defined sequential computational technique that accepts a value or a collection of values as input and produces the output(s) needed to solve a problem. 

Or we can say that an algorithm is said to be accurate if and only if it stops with the proper output for each input instance. 


Algorithms are used to solve problems or automate tasks in a systematic and efficient manner. They are a set of instructions or rules that guide the computer or software in performing a particular task or solving a problem.

There are several reasons why we use algorithms:

  • Efficiency: Algorithms can perform tasks quickly and accurately, making them an essential tool for tasks that require a lot of calculations or data processing.
  • Consistency: Algorithms are repeatable and produce consistent results every time they are executed. This is important when dealing with large amounts of data or complex processes.
  • Scalability: Algorithms can be scaled up to handle large datasets or complex problems, which makes them useful for applications that require processing large volumes of data.
  • Automation: Algorithms can automate repetitive tasks, reducing the need for human intervention and freeing up time for other tasks.
  • Standardization: Algorithms can be standardized and shared among different teams or organizations, making it easier for people to collaborate and share knowledge.

Overall, algorithms are an essential tool for solving problems in a variety of fields, including computer science, engineering, data analysis, finance, and many others.


Consider a box where no one can see what’s happening inside, we say a black box. 

We give input to the box and it gives us the output we need but the procedure that we might need to know behind the conversion of input to desired output is an ALGORITHM. 

An algorithm is independent of the language used. It tells the programmer the logic used to solve the problem. So, it is a logical step-by-step procedure that acts as a blueprint to programmers.

Real-life examples that define the use of algorithms:

  • Consider a clock. We know the clock is ticking but how does the manufacturer set those nuts and bolts so that it keeps on moving every 60 seconds, the min hand should move and every 60 mins, the hour hand should move? So to solve this problem, there must be an algorithm behind it.
  • Seen someone cooking your favorite food for you? Is the recipe necessary for it? Yes, it is necessary as a recipe is a sequential procedure that turns a raw potato into a chilly potato. This is what an algorithm is: following a procedure to get the desired output. Is the sequence necessary to be followed? Yes, the sequence is the most important thing that has to be followed to get what we want.

Types of Algorithms:

  • Sorting algorithms: Bubble Sort, insertion sort, and many more. These algorithms are used to sort the data in a particular format.
  • Searching algorithms: Linear search, binary search, etc. These algorithms are used in finding a value or record that the user demands.
  • Graph Algorithms: It is used to find solutions to problems like finding the shortest path between cities, and real-life problems like traveling salesman problems.

Sorting algorithms are algorithms that take a collection of elements and rearrange them in a specified order (e.g. ascending or descending). There are many different sorting algorithms, each with its own strengths and weaknesses. Some of the most commonly used sorting algorithms include:

Bubble sort: A simple sorting algorithm that repeatedly steps through the list, compares adjacent elements and swaps them if they are in the wrong order.

Insertion sort: A simple sorting algorithm that builds up the final sorted array one item at a time, by comparing each new item to the items that have already been sorted and inserting it in the correct position.

Selection sort: A simple sorting algorithm that repeatedly selects the minimum element from the unsorted part of the array and moves it to the end of the sorted part.

Merge sort: A divide-and-conquer sorting algorithm that works by dividing the unsorted list into n sub-lists, sorting each sub-list, and then merging them back into a single sorted list.

Quick sort: A divide-and-conquer sorting algorithm that works by selecting a “pivot” element from the array and partitioning the other elements into two sub-arrays, according to whether they are less than or greater than the pivot. The sub-arrays are then sorted recursively.

Each of these algorithms has different time and space complexities, making some more suitable for certain use cases than others.

Searching algorithms are algorithms that search for a particular element or value in a data structure (such as an array or a linked list). Some of the most commonly used searching algorithms include:

Linear search: A simple searching algorithm that iterates through every element of a list until it finds a match.

Binary search: A searching algorithm that works by dividing a sorted list in half repeatedly, until the desired element is found or it can be determined that the element is not present.

Jump search: A searching algorithm that works by jumping ahead by fixed steps in the list, until a suitable candidate is found, and then performing a linear search in the surrounding elements.

Interpolation search: A searching algorithm that works by using information about the range of values in the list to estimate the position of the desired element and then verifying that it is indeed present.

Hash table search: A searching algorithm that uses a hash function to map elements to indices in an array, and then performs constant-time lookups in the array to find the desired element.

Each of these algorithms has different time and space complexities, making some more suitable for certain use cases than others. The choice of which algorithm to use depends on the specific requirements of the problem, such as the size of the data structure, the distribution of values, and the desired time complexity.

Graph algorithms are a set of algorithms that are used to process, analyze and understand graph data structures. Graphs are mathematical structures used to model relationships between objects, where the objects are represented as vertices (or nodes) and the relationships between them are represented as edges. Graph algorithms are used in a variety of applications such as network analysis, social network analysis, recommendation systems, and in many other areas where understanding the relationships between objects is important. Some of the common graph algorithms include:

Shortest Path algorithms (e.g. Dijkstra’s, Bellman-Ford, A*)
Minimum Spanning Tree algorithms (e.g. Kruskal, Prim)
Maximum Flow algorithms (e.g. Ford-Fulkerson, Edmonds-Karp)
Network Flow algorithms (e.g. Bipartite Matching)
Connectivity algorithms (e.g. Depth-first Search, Breadth-first Search)

Why do we use algorithms?

Consider two kids, Aman and Rohan, solving the Rubik’s Cube. Aman knows how to solve it in a definite number of steps. On the other hand, Rohan knows that he will do it but is not aware of the procedure. Aman solves the cube within 2 minutes whereas Rohan is still stuck and by the end of the day, he somehow managed to solve it (might have cheated as the procedure is necessary). 

So the time required to solve with a procedure/algorithm is much more effective than that without any procedure. Hence the need for an algorithm is a must. 

In terms of designing a solution to an IT problem, computers are fast but not infinitely fast. The memory may be inexpensive but not free. So, computing time is therefore a bounded resource and so is the space in memory. So we should use these resources wisely and algorithms that are efficient in terms of time and space will help you do so. 

Creating an Algorithm:

Since the algorithm is language-independent, we write the steps to demonstrate the logic behind the solution to be used for solving a problem. But before writing an algorithm, keep the following points in mind:

  • The algorithm should be clear and unambiguous.
  • There should be 0 or more well-defined inputs in an algorithm.
  • An algorithm must produce one or more well-defined outputs that are equivalent to the desired output. After a specific number of steps, algorithms must ground to a halt.
  • Algorithms must stop or end after a finite number of steps.
  • In an algorithm, step-by-step instructions should be supplied, and they should be independent of any computer code.

Example: algorithm to multiply 2 numbers and print the result:

Step 1: Start
Step 2: Get the knowledge of input. Here we need 3 variables; a and b will be the user input and c will hold the result.  
Step 3: Declare a, b, c variables.
Step 4: Take input for a and b variable from the user.
Step 5: Know the problem and find the solution using operators, data structures and logic

We need to multiply a and b variables so we use * operator and assign the result to c. 
That is c <- a * b

Step 6: Check how to give output, Here we need to print the output. So write print c
Step 7: End

Example 1: Write an algorithm to find the maximum of all the elements present in the array.
Follow the algorithm approach as below:

Step 1: Start the Program
Step 2: Declare a variable max with the value of the first element of the array.
Step 3: Compare max with other elements using loop.
Step 4: If max < array element value, change max to new max.
Step 5: If no element is left, return or print max otherwise goto step 3.
Step 6: End of Solution

Example 2: Write an algorithm to find the average of 3 subjects. 
Follow the algorithm approach as below:

Step 1: Start the Program
Step 2: Declare and Read 3 Subject, let’s say S1, S2, S3
Step 3: Calculate the sum of all the 3 Subject values and store result in Sum variable (Sum = S1+S2+S3)
Step 4: Divide Sum by 3 and assign it to Average variable. (Average = Sum/3)
Step 5: Print the value of Average of 3 Subjects
Step 6: End of Solution

Know about Algorithm Complexity:

Complexity in algorithms refers to the amount of resources (such as time or memory) required to solve a problem or perform a task. The most common measure of complexity is time complexity, which refers to the amount of time an algorithm takes to produce a result as a function of the size of the input. Memory complexity refers to the amount of memory used by an algorithm. Algorithm designers strive to develop algorithms with the lowest possible time and memory complexities, since this makes them more efficient and scalable.

The complexity of an algorithm is a function describing the efficiency of the algorithm in terms of the amount of data the algorithm must process.

Usually there are natural units for the domain and range of this function.

An algorithm is analyzed using Time Complexity and Space Complexity. Writing an efficient algorithm help to consume the minimum amount of time for processing the logic. For algorithm A, it is judged on the basis of two parameters for an input of size n :

  • Time Complexity: Time taken by the algorithm to solve the problem. It is measured by calculating the iteration of loops, number of comparisons etc.
  • Time complexity is a function describing the amount of time an algorithm takes in terms of the amount of input to the algorithm.
  • “Time” can mean the number of memory accesses performed, the number of comparisons between integers, the number of times some inner loop is executed, or some other natural unit related to the amount of real time the algorithm will take.
  • Space Complexity: Space taken by the algorithm to solve the problem. It includes space used by necessary input variables and any extra space (excluding the space taken by inputs) that is used by the algorithm. For example, if we use a hash table (a kind of data structure), we need an array to store values so 
  • this is an extra space occupied, hence will count towards the space complexity of the algorithm. This extra space is known as Auxiliary Space.
  • Space complexity is a function describing the amount of memory(space)an algorithm takes in terms of the amount of input to the algorithm.
  • Space complexity is sometimes ignored because the space used is minimal and/ or obvious, but sometimes it becomes an issue as time.

.The time complexity of the operations:

  • The choice of data structure should be based on the time complexity of the operations that will be performed.
  • Time complexity is defined in terms of how many times it takes to run a given algorithm, based on the length of the input.
  • The time complexity of an algorithm is the amount of time it takes for each statement to complete. It is highly dependent on the size of the processed data.
  • For example, if you need to perform searches frequently, you should use a binary search tree.

.The space complexity of the operations:

  • The choice of data structure should be based on the space complexity of the operations that will be performed.
  • The amount of memory used by a program to execute it is represented by its space complexity.
  • Because a program requires memory to store input data and temporal values while running , the space complexity is auxiliary and input space.
  • For example, if you need to store a lot of data, you should use an array.

cases in complexities:

There are two commonly studied cases of complexity in algorithms:

1.Best case complexity: The best-case scenario for an algorithm is the scenario in which the algorithm performs the minimum amount of work (e.g. takes the shortest amount of time, uses the least amount of memory, etc.).

2.Worst case complexity: The worst-case scenario for an algorithm is the scenario in which the algorithm performs the maximum amount of work (e.g. takes the longest amount of time, uses the most amount of memory, etc.).

In analyzing the complexity of an algorithm, it is often more informative to study the worst-case scenario, as this gives a guaranteed upper bound on the performance of the algorithm. Best-case scenario analysis is sometimes performed, but is generally less important as it provides a lower bound that is often trivial to achieve.

Advantages of Algorithms

  • Easy to understand: Since it is a stepwise representation of a solution to a given problem, it is easy to understand.
  • Language Independent: It is not dependent on any programming language, so it can easily be understood by anyone.
  • Debug / Error Finding: Every step is independent / in a flow so it will be easy to spot and fix the error.
  • Sub-Problems: It is written in a flow so now the programmer can divide the tasks which makes them easier to code.

Disadvantages of Algorithms

  • Creating efficient algorithms is time-consuming and requires good logical skills.
  • Nasty to show branching and looping in algorithms.

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