how to sort a list without build-in function

Question

I want to sort a list like below.Without using the build-in function so I tried this:

    sort[n_] := 
     Module[{n0 = n, i, j}, 
      Do[Do[If[n[[j - 1]] > 
           n[[j]], {n[[j - 1]], n[[j]]} = {n[[j]], n[[j - 1]]}],
         {j, Length[n], i, -1}];
       , {i, 1, Length[n] - 1}]; n]
l = {2, 1, 1, 10, 9, 8, 1};sort[l]

But it seem my code is not correct.Can Anyone help me to figure out this. Any hints or solution will be appreciated.

Answer 1

Your code is - nearly - ok. But you return ninstead of n0 and you should work on a temporary variable (n0or here temp). It is always a good idea to use variable names that are (a bit) self explanatory. So make something like:

  sort[list_] := 
     Module[{temp = list, i, j}, 
      Do[Do[If[temp[[j - 1]] > 
           temp[[j]], {temp[[j - 1]], temp[[j]]} = {temp[[j]], temp[[j - 1]]}],
         {j, Length[temp], i, -1}];
       , {i, 1, Length[temp] - 1}]; temp]

I have changed only variable names, for me more easy to read. But.... Bubblesort is one of the worst you can take.

Edit I forgot to mention, that you can implement Bubblesort in a rule-based approach in a oneliner (it is O(n^3), but nice)

bubbleRule[xs___, x_, y_, ys___] := bubbleRule[xs, y, x, ys] /; x > y

Then bubbleRule @ list sorts list ;-)