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    <p>If the purpose is just to generate a random permutation, I don't really understand the need for sorting. The following code runs in linear time as far as I can tell</p> <pre><code>public static int[] getRandomPermutation (int length){ // initialize array and fill it with {0,1,2...} int[] array = new int[length]; for(int i = 0; i &lt; array.length; i++) array[i] = i; for(int i = 0; i &lt; length; i++){ // randomly chosen position in array whose element // will be swapped with the element in position i // note that when i = 0, any position can chosen (0 thru length-1) // when i = 1, only positions 1 through length -1 // NOTE: r is an instance of java.util.Random int ran = i + r.nextInt (length-i); // perform swap int temp = array[i]; array[i] = array[ran]; array[ran] = temp; } return array; } </code></pre> <p>And here is some code to test it:</p> <pre><code>public static void testGetRandomPermutation () { int length =4; // length of arrays to construct // This code tests the DISTRIBUTIONAL PROPERTIES ArrayList&lt;Integer&gt; counts = new ArrayList &lt;Integer&gt; (); // filled with Integer ArrayList&lt;int[]&gt; arrays = new ArrayList &lt;int[]&gt; (); // filled with int[] int T = 1000000; // number of trials for (int t = 0; t &lt; T; t++) { int[] perm = getRandomPermutation(length); // System.out.println (getString (perm)); boolean matchFound = false; for(int j = 0; j &lt; arrays.size(); j++) { if(equals(perm,arrays.get(j))) { //System.out.println ("match found!"); matchFound = true; // increment value of count in corresponding position of count list counts.set(j, Integer.valueOf(counts.get(j).intValue()+1)); break; } } if (!matchFound) { arrays.add(perm); counts.add(Integer.valueOf(1)); } } for(int i = 0; i &lt; arrays.size(); i++){ System.out.println (getString (arrays.get (i))); System.out.println ("frequency: " + counts.get (i).intValue ()); } // Now let's test the speed T = 500000; // trials per array length n // n will the the length of the arrays double[] times = new double[97]; for(int n = 3; n &lt; 100; n++){ long beginTime = System.currentTimeMillis(); for(int t = 0; t &lt; T; t++){ int[] perm = getRandomPermutation(n); } long endTime = System.currentTimeMillis(); times[n-3] = (double)(endTime-beginTime); System.out.println("time to make "+T+" random permutations of length "+n+" : "+ (endTime-beginTime)); } // Plotter.plot(new double[][]{times}); } </code></pre>
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