all tasks

Task/Sorting-algorithms-Permutation-sort/E/sorting-algorithms-permutation-sort.e

@@ -0,0 +1,40 @@
+def swap(container, ixA, ixB) {
+    def temp := container[ixA]
+    container[ixA] := container[ixB]
+    container[ixB] := temp
+}
+
+/** Reverse order of elements of 'sequence' whose indexes are in the interval [ixLow, ixHigh] */
+def reverseRange(sequence, var ixLow, var ixHigh) {
+    while (ixLow < ixHigh) {
+        swap(sequence, ixLow, ixHigh)
+        ixLow += 1
+        ixHigh -= 1
+    }
+}
+
+/** Algorithm from <http://marknelson.us/2002/03/01/next-permutation>, allegedly from a version of the C++ STL */
+def nextPermutation(sequence) {
+    def last := sequence.size() - 1
+    var i := last
+    while (true) {
+        var ii := i
+        i -= 1
+        if (sequence[i] < sequence[ii]) {
+            var j := last + 1
+            while (!(sequence[i] < sequence[j -= 1])) {} # buried side effect
+            swap(sequence, i, j)
+            reverseRange(sequence, ii, last)
+            return true
+        }
+        if (i == 0) {
+            reverseRange(sequence, 0, last)
+            return false
+        }
+    }
+}
+
+/** Note: Worst case on sorted list */
+def permutationSort(flexList) {
+    while (nextPermutation(flexList)) {}
+}