How do you calculate space complexity?

Answer 1

Calculate the amount of additional memory used by the algorithm relative to the number of its inputs. Typically the number of inputs is defined by a container object or data sequence of some type, such as an array. If the amount of memory consumed remains the same regardless of the number of inputs, then the space complexity is constant, denoted O(1) in Big-Omega notation (Big-O). If the amount of memory consumed increases linearly as n increases, then the space complexity is O(n).

For example, the algorithm that sums a data sequence has O(1) space complexity because the number of inputs does not affect the amount of additional memory consumed by the accumulator. However, the algorithm which copies a data sequence of n elements has a space complexity of O(n) because the algorithm must allocate n elements to store the copy.

Other commonly used complexities include O(n*n) to denote quadratic complexity and O(log n) to denote (binary) logarithmic complexity. Combinations of the two are also permitted, such as O(n log n).