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Task/Sorting-algorithms-Heapsort/ALGOL-68/sorting-algorithms-heapsort.alg

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+#--- Swap function ---#
+PROC swap = (REF []INT array, INT first, INT second) VOID:
+(
+    INT temp := array[first];
+    array[first] := array[second];
+    array[second]:= temp
+);
+
+#--- Heap sort Move Down ---#
+PROC heapmove = (REF []INT array, INT i, INT last) VOID:
+(
+    INT index := i;
+    INT larger := (index*2);
+
+    WHILE larger <= last DO
+        IF larger < last THEN IF array[larger] < array[larger+1] THEN
+            larger +:= 1
+        FI FI;
+        IF array[index] < array[larger] THEN
+            swap(array, index, larger)
+        FI;
+        index := larger;
+        larger := (index*2)
+    OD
+);
+
+#--- Heap sort ---#
+PROC heapsort = (REF []INT array) VOID:
+(
+    FOR i FROM ENTIER((UPB array) / 2) BY -1 WHILE
+        heapmove(array, i, UPB array);
+    i > 1 DO SKIP OD;
+
+    FOR i FROM UPB array BY -1 WHILE
+        swap(array, 1, i);
+        heapmove(array, 1, i-1);
+    i > 1 DO SKIP OD
+);
+#***************************************************************#
+main:
+(
+    [10]INT a;
+    FOR i FROM 1 TO UPB a DO
+        a[i] := ROUND(random*100)
+    OD;
+
+    print(("Before:", a));
+    print((newline, newline));
+    heapsort(a);
+    print(("After: ", a))
+
+)