Which of the following statements is/are valid and example in depth? 1. Time Complexity of QuickSort is (n^2) 2. Time Complexity of QuickSort is O(n^2) 3. For any two functions f(n) and g(n), we have f(n) = (g(n)) if and only if f(n) = O(g(n)) and f(n) = (g(n)). 4. Time complexity of all computer algorithms can be written as (1)