As you were writing Bubble Sort, you may have realized that we were doing some unnecessary iterations.

Consider the first pass through the outer loop. We’re making `n-1`

comparisons.

nums = [5, 4, 3, 2, 1] # 5 element list: N is 5 bubble_sort(nums) # 5 > 4 # [4, 5, 3, 2, 1] # 5 > 3 # [4, 3, 5, 2, 1] # 5 > 2 # [4, 3, 2, 5, 1] # 5 > 1 # [4, 3, 2, 1, 5] # four comparisons total

We know the last value in the list is in its correct position, so **we never need to consider it again**. The second time through the loop, we only need `n-2`

comparisons.

As we correctly place more values, fewer elements need to be compared. An optimized version doesn’t make `n^2-n`

comparisons, it does `(n-1) + (n-2) + ... + 2 + 1`

comparisons, which can be simplified to `(n^2-n) / 2`

comparisons.

This is fewer than `n^2-n`

comparisons but the algorithm still has a big O runtime of `O(N^2)`

.

As the input, `N`

, grows larger, the division by two has less significance. Big O considers inputs **as they reach infinity** so the higher order term `N^2`

completely dominates.

We can’t make Bubble Sort better than `O(N^2)`

, but let’s take a look at the optimized code and compare iterations between implementations!

We’re also taking advantage of parallel assignment in Python and abstracting away the `swap()`

function!

### Instructions

Run the code and marvel at the increased efficiency!

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