What Is Time and Space Complexity in Data Structure With Example?


Angela Bailey

Time and space complexity are important concepts in the field of data structures and algorithms. They help us analyze the efficiency of an algorithm and understand how it performs as the size of the input increases. In this article, we will explore what time and space complexity mean and how they can be calculated, along with some examples to illustrate these concepts.

Time Complexity

In simple terms, time complexity refers to the amount of time an algorithm takes to run as a function of the size of its input. It helps us understand how the runtime of an algorithm grows with respect to the input size.

Time complexity is commonly represented using Big O notation, which provides an upper bound on how long an algorithm will take to run. Here are some common time complexities:

  • O(1): Constant Time
  • O(log n): Logarithmic Time
  • O(n): Linear Time
  • O(n log n): Linearithmic Time
  • O(n^2): Quadratic Time
  • O(2^n): Exponential Time

Let’s consider an example to understand time complexity better. Suppose we have an array of numbers and we want to find if a specific number is present in the array:

function search(arr, Target) {
   for (let i = 0; i < arr.length; i++) {
      if (arr[i] === Target) {
         return true;
   return false;

In this case, we iterate through each element in the array until we find the Target number or reach the end. If the Target number is present, the algorithm will have a time complexity of O(n) in the worst case, where n is the size of the array. This means that the time taken to find the Target number increases linearly with the size of the array.

Space Complexity

Space complexity refers to the amount of memory an algorithm needs to run as a function of its input size. It helps us understand how much additional memory an algorithm requires to store variables, data structures, and other resources.

Similar to time complexity, space complexity is represented using Big O notation. Here are some common space complexities:

  • O(1): Constant Space
  • O(n): Linear Space
  • O(n^2): Quadratic Space

Let's consider another example to understand space complexity. Suppose we have a function that generates all possible permutations of a given string:

function generatePermutations(str) {
   let result = [];
   permute(str, '', result);
   return result;

function permute(str, prefix, result) {
   if (str.length === 0) {

   for (let i = 0; i < str.length; i++) {
      let char = str[i];
      let rest = str.substring(0, i) + str.substring(i + 1);
      permute(rest, prefix + char, result);

In this case, we use a recursive approach to generate all possible permutations of the given string. The space complexity of this algorithm will be O(n!

), where n is the length of the input string. This is because for each character in the string, we create a new recursive call, resulting in an exponential growth of function calls and memory usage.


Understanding time and space complexity is crucial when designing algorithms or analyzing their performance. By considering these factors, we can make informed decisions about selecting the most efficient algorithms for our needs.

In this article, we explored what time and space complexity mean and how they can be calculated. We also examined some examples to illustrate these concepts. Remember to take into account both time and space complexity when evaluating the efficiency of an algorithm in order to make optimal choices in your programming endeavors.

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