Time complexity of bubble sort
In Bubble Sort, n-1 comparisons will be done in 1st iteration, n-2 in 2nd iteration, n-3 in 3rd iteration and so on. So the total number of comparisons will be
sum = n(n-1)/2
So the time complexity of bubble sort is o(n2).
Time complexity of bubble sort in best case will be o(n).
Time complexity of insertion sort
If we take a closer look at the insertion sort code, we can notice that every iteration of while loop reduces one inversion. The while loop executes only if i > j and arr[i] < arr[j]. Therefore total number of while loop iterations (For all values of i) is same as number of inversions. Therefore overall time complexity of the insertion sort is O(n + f(n)) where f(n) is inversion count. If the inversion count is O(n), then the time complexity of insertion sort in best case is O(n). In worst case, there can be n*(n-1)/2 inversions. The worst case occurs when the array is sorted in reverse order. So the worst case time complexity of insertion sort is O(n2).