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POmergesort - with an insignificant change throws SystemInvalidOperationException
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  1. POmergesort - with an insignificant change throws SystemInvalidOperationException
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    copied!<p>A very strange thing occured in my program. Here is the simplified code.</p> <pre><code>class Program { static void Main(string[] args) { ArrayList numbers = new ArrayList(); numbers.Add(1); numbers.Add(3); numbers.Add(4); numbers.Add(2); var it = Sorts.MergeSort((ArrayList)numbers.Clone()); Sorts.PrintArray(it, "mergesort"); Console.WriteLine("DONE"); Console.ReadLine(); } } public static class Sorts { public static ArrayList BubbleSort(ArrayList numbers) { bool sorted = true; for (int i = 0; i &lt; numbers.Count; i++) { for (int j = 1; j &lt; numbers.Count; j++) { if ((int)numbers[j - 1] &gt; (int)numbers[j]) { int tmp = (int)numbers[j - 1]; numbers[j - 1] = numbers[j]; numbers[j] = tmp; sorted = false; } } if (sorted) { return numbers; } } return numbers; } public static ArrayList MergeSort(ArrayList numbers, int switchLimit = 3) { //if I use this if - everything works if (numbers.Count &lt;= 1) { // return numbers; } //the moment I use this condition - it throws SystemInvalidOperationException in function Merge in the line of a "for"-loop if (numbers.Count &lt;=switchLimit) { return Sorts.BubbleSort(numbers); } ArrayList ret = new ArrayList(); int middle = numbers.Count / 2; ArrayList L = numbers.GetRange(0, middle); ArrayList R = numbers.GetRange(middle, numbers.Count - middle); L = MergeSort(L); R = MergeSort(R); return Merge(L, R); } private static ArrayList Merge(ArrayList L, ArrayList R) { ArrayList ret = new ArrayList(); int l = 0; int r = 0; for (int i = 0; i &lt; L.Count + R.Count; i++) { if (l == L.Count) { ret.Add(R[r++]); } else if (r == R.Count) { ret.Add(L[l++]); } else if ((int)L[l] &lt; (int)R[r]) { ret.Add(L[l++]); } else { ret.Add(R[r++]); } } return ret; } //--------------------------------------------------------------------------------- public static void PrintArray(ArrayList arr, string txt = "", int sleep = 0) { Console.WriteLine("{1}({0}): ", arr.Count, txt); for (int i = 0; i &lt; arr.Count; i++) { Console.WriteLine(arr[i].ToString().PadLeft(10)); } Console.WriteLine(); System.Threading.Thread.Sleep(sleep); } } </code></pre> <p>There is a problem with my Sorts.MergeSort function. When I use it normally (take a look at the first if-condition in a function - all works perfectly. But the moment when I want it to switch to bubblesort with smaller input (the second if-condition in the function) it throws me an SystemInvalidOperationException. I have no idea where is the problem. Do you see it? Thanks. :) Remark: bubblesort itself works - so there shouldn't be a problem in that sort...</p>
 

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