September Morn Update

Task/Forward-difference/ALGOL-W/forward-difference.alg

@@ -0,0 +1,31 @@
+begin
+    % calculate forward differences                                  %
+
+    % sets elements of B to the first order forward differences of A %
+    % A should have bounds 1 :: n, B should have bounds 1 :: n - 1   %
+    procedure FirstOrderFDifference ( integer array A( * )
+                                    ; integer array B( * )
+                                    ; integer value n
+                                    ) ;
+        for i := 2 until n do B( i - 1 ) := A( i ) - A( i - 1 );
+
+    integer array v   ( 1 :: 10 );
+    integer array diff( 1 ::  9 );
+    integer vPos, length;
+
+    % construct the initial values array                              %
+    vPos := 1;
+    for i := 90, 47, 58, 29, 22, 32, 55, 5, 55, 73 do begin
+        v( vPos ) := i;
+        vPos := vPos + 1
+    end for_i ;
+    % calculate and show the differences                              %
+    i_w    := 5; % set output format %
+    length := 10;
+    for order := 1 until length - 1 do begin
+        FirstOrderFDifference( v, diff, length );
+        length := length - 1;
+        write( order, ": " ); for i := 1 until length do writeon( diff( i ) );
+        for i := 1 until length do v( i ) := diff( i )
+    end for_order
+end.

Task/Forward-difference/Dart/forward-difference.dart

@@ -0,0 +1,17 @@
+List forwardDifference(List _list) {
+  for (int i = _list.length - 1; i > 0; i--) {
+    _list[i] = _list[i] - _list[i - 1];
+  }
+
+  _list.removeRange(0, 1);
+  return _list;
+}
+
+void mainAlgorithms() {
+  List _intList = [90, 47, 58, 29, 22, 32, 55, 5, 55, 73];
+
+  for (int i = _intList.length - 1; i >= 0; i--) {
+    List _list = forwardDifference(_intList);
+    print(_list);
+  }
+}

Task/Forward-difference/Swift/forward-difference.swift

@@ -0,0 +1,20 @@
+func forwardsDifference<T: SignedNumeric>(of arr: [T]) -> [T] {
+  return zip(arr.dropFirst(), arr).map({ $0.0 - $0.1 })
+}
+
+func nthForwardsDifference<T: SignedNumeric>(of arr: [T], n: Int) -> [T] {
+  assert(n >= 0)
+
+  switch (arr, n) {
+  case ([], _):
+    return []
+  case let (arr, 0):
+    return arr
+  case let (arr, i):
+    return nthForwardsDifference(of: forwardsDifference(of: arr), n: i - 1)
+  }
+}
+
+for diff in (0...9).map({ nthForwardsDifference(of: [90, 47, 58, 29, 22, 32, 55, 5, 55, 73], n: $0) }) {
+  print(diff)
+}