September Morn Update

Task/Sorting-algorithms-Merge-sort/Dart/sorting-algorithms-merge-sort.dart

@@ -1,54 +1,118 @@
-merge(left, right, items) {
-  var a = 0;
-  var t;
-
-  while (left.length != 0 && right.length != 0) {
-    if (right[0] < left[0]) {
-     t = right[0];
-     right.removeRange(0,1);
-    } else {
-      t = left[0];
-      left.removeRange(0,1);
-    }
-    items[a++] = t;
-  }
-
-  while(left.length != 0) {
-    t = left[0];
-    left.removeRange(0,1);
-    items[a++] = t;
-  }
-
-  while(right.length != 0) {
-    t = right[0];
-    right.removeRange(0,1);
-    items[a++] = t;
-  }
-}
-
-mSort(items, tmp, l) {
-  if (l == 1) {
-    return;
-  }
-
-  var m = (l/2).floor().toInt();
-  var tmp_l = tmp.getRange(0, m);
-  var tmp_r = tmp.getRange(m, tmp.length-m);
-
-  mSort(tmp_l, items.getRange(0,m), m);
-  mSort(tmp_r, items.getRange(m, items.length-m), l-m);
-  merge(tmp_l, tmp_r, items);
-}
-
-merge_sort(items) {
-  mSort(items,items.getRange(0, items.length),items.length);
-}
-
 void main() {
-  var arr=[1,5,2,7,3,9,4,6,8];
-  print("Before sort");
-  arr.forEach((var i)=>print("$i"));
-  merge_sort(arr);
-  print("After sort");
-  arr.forEach((var i)=>print("$i"));
+  MergeSortInDart sampleSort = MergeSortInDart();
+
+  List<int> theResultingList = sampleSort.sortTheList([54, 89, 125, 47899, 32, 61, 42, 895647, 215, 345, 6, 21, 2, 78]);
+
+  print('Here\'s the sorted list: ${theResultingList}');
+}
+
+/////////////////////////////////////
+
+class MergeSortInDart {
+
+  List<int> sortedList;
+
+  // In Dart we often put helper functions at the bottom.
+  // You could put them anywhere, we just like it this way
+  // for organizational purposes. It's nice to be able to
+  // read them in the order they're called.
+
+  // Start here
+  List<int> sortTheList(List<int> sortThis){
+    // My parameters are listed vertically for readability. Dart
+    // doesn't care how you list them, vertically or horizontally.
+    sortedList = mSort(
+      sortThis,
+      sortThis.sublist(0, sortThis.length),
+      sortThis.length,
+    );
+    return sortThis;
+  }
+
+  mSort(
+    List<int> sortThisList,
+    List<int> tempList,
+    int thisListLength) {
+
+    if (thisListLength == 1) {
+      return;
+    }
+
+    // In Dart using ~/ is more efficient than using .floor()
+    int middle = (thisListLength ~/ 2);
+
+    // If you use something in a try/on/catch/finally block then
+    // be sure to declare it outside the block (for scope)
+    List<int> tempLeftList;
+
+    // This was used for troubleshooting. It was left here to show
+    // how a basic block try/on can be better than a debugPrint since
+    // it won't print unless there's a problem.
+    try {
+      tempLeftList = tempList.sublist(0, middle);
+    } on RangeError {
+      print(
+          'tempLeftList length = ${tempList.length}, thisListLength '
+            'was supposedly $thisListLength and Middle was $middle');
+    }
+
+    // If you see "myList.getRange(x,y)" that's a sign the code is
+    // from Dart 1 and needs to be updated. It's "myList.sublist" in Dart 2
+    List<int> tempRightList = tempList.sublist(middle);
+
+    // Left side.
+    mSort(
+      tempLeftList,
+      sortThisList.sublist(0, middle),
+      middle,
+    );
+
+    // Right side.
+    mSort(
+      tempRightList,
+      sortThisList.sublist(middle),
+      sortThisList.length - middle,
+    );
+
+    // Merge it.
+    dartMerge(
+      tempLeftList,
+      tempRightList,
+      sortThisList,
+    );
+  }
+
+  dartMerge(
+    List<int> leftSide,
+    List<int> rightSide,
+    List<int> sortThisList,
+    ) {
+    int index = 0;
+    int elementValue;
+
+    // This should be human readable.
+    while (leftSide.isNotEmpty && rightSide.isNotEmpty) {
+      if (rightSide[0] < leftSide[0]) {
+        elementValue = rightSide[0];
+        rightSide.removeRange(0, 1);
+      } else {
+        elementValue = leftSide[0];
+        leftSide.removeRange(0, 1);
+      }
+      sortThisList[index++] = elementValue;
+    }
+
+    while (leftSide.isNotEmpty) {
+      elementValue = leftSide[0];
+      leftSide.removeRange(0, 1);
+      sortThisList[index++] = elementValue;
+    }
+
+    while (rightSide.isNotEmpty) {
+      elementValue = rightSide[0];
+      rightSide.removeRange(0, 1);
+      sortThisList[index++] = elementValue;
+    }
+    sortedList = sortThisList;
+  }
 }