Corrected grammatical and typographical errors in cheat sheet

[jayathuc]

Asymptotic Notation Correction: "Big-O refers to the upper bound of time or space complexity of an algorithm, meaning it worst case runtime scenario." Updated: "Big-O refers to the upper bound of time or space complexity of an algorithm, typically representing the worst-case runtime scenario."

Typo: "Best case means a ideal input." Updated: "Best case means an ideal input."

Search Algorithms - Depth First Search Correction: "It traverses left down a tree until it cannot go further." Updated: "It traverses down the left side of a tree until it cannot go further."

Sorting Algorithms - Insertion Sort Correction: "Although it has an O(n^2) time complexity, in practice it "is slightly less" since its comparison scheme only requires checking place if it is smaller than its neighbor." Updated: "Although it has an O(n^2) time complexity, in practice it "can perform better" since its comparison scheme only requires checking place if it is smaller than its neighbor."

Sorting Algorithms - Merge Sort Correction: "Worst Case: O(1)" Updated: "Worst Case: O(n)" (because merge sort requires additional space proportional to the input size.)