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Task/Sorting-algorithms-Heapsort/Sidef/sorting-algorithms-heapsort.sidef

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+func sift_down(a, start, end) {
+    var root = start;
+    while ((2*root + 1) <= end) {
+        var child = (2*root + 1);
+        if ((child+1 <= end) && (a[child] < a[child + 1])) {
+            child += 1;
+        }
+        if (a[root] < a[child]) {
+            a[child, root] = a[root, child];
+            root = child;
+        } else {
+            return;
+        }
+    }
+}
+
+func heapify(a, count) {
+    var start = ((count - 2) / 2);
+    while (start >= 0) {
+        sift_down(a, start, count-1);
+        start -= 1;
+    }
+}
+
+func heap_sort(a, count) {
+    heapify(a, count);
+    var end = (count - 1);
+    while (end > 0) {
+        a[0, end] = a[end, 0];
+        end -= 1;
+        sift_down(a, 0, end)
+    }
+    return a
+}
+
+var arr = (1..10 -> shuffle);  # creates a shuffled array
+say arr;                       # prints the unsorted array
+heap_sort(arr, arr.len);       # sorts the array in-place
+say arr;                       # prints the sorted array