src/Grid.cpp

@@ -1,6 +1,6 @@
 #include "Grid.h"
 
-#include <stdlib.h>
+#include "Random.h"
 
 Grid::Grid(int8 dimension)
 {
@@ -12,7 +12,6 @@ void Grid::SetDimension(int8 dimension)
 	fDimension = dimension;
 	fData.clear();
 	fData.resize(dimension * dimension, 0);
-	fGrid = fData;
 }
 
 
@@ -24,11 +23,11 @@ void Grid::SetDimension(int8 dimension)
 
 void Grid::Random(int8 minMoves)
 {
-	const int8 numButtons = fGrid.size();
+	const int8 numButtons = fData.size();
 
 	// start with an empty grid
 	for (int8 index = 0; index < numButtons; index++)
-		fData[index] = fGrid[index] = 0;
+		fData[index] = 0;
 
 	/*
 	 * Some of the eigenvectors
@@ -71,35 +70,31 @@ void Grid::Random(int8 minMoves)
 	if (minMoves > numButtons)
 		minMoves = numButtons;
 
-	for (int8 count = 0; count < minMoves; count++) {
-		int8 index;
+	int buttonIndices[numButtons];
 
-		// next random button not already marked
-		do
-			index = random() % numButtons;
-		while (fGrid[index]);
-
-		fGrid[index] = 1;	// mark the button to be pressed
-	}
+	for (int8 index = 0; index < numButtons; index++)
+		buttonIndices[index] = index;
 
+	const int8 begin = ChooseRandom(buttonIndices, numButtons, minMoves);
 	const int8 n = fDimension;
 
-	for (int8 index = 0; index < numButtons; index++)
-		if (fGrid[index]) {
-			if (index % n)	// not leftmost column
-				fData[index - 1] = !fData[index - 1];	// left neighbor
+	for (int8 i = 0; i < minMoves; i++) {
+		const int8 index = buttonIndices[begin + i];
+
+		if (index % n)	// not leftmost column
+			fData[index - 1] = !fData[index - 1];	// left neighbor
 
-			if ((index + 1) % n)	// not rightmost column
-				fData[index + 1] = !fData[index + 1];	// right neighbor
+		if ((index + 1) % n)	// not rightmost column
+			fData[index + 1] = !fData[index + 1];	// right neighbor
 
-			if (index >= n)	// not top row
-				fData[index - n] = !fData[index - n];	// neighbor above
+		if (index >= n)	// not top row
+			fData[index - n] = !fData[index - n];	// neighbor above
 
-			if (index < n * (n - 1))	// not bottom row
-				fData[index + n] = !fData[index + n];	// neighbor below
+		if (index < n * (n - 1))	// not bottom row
+			fData[index + n] = !fData[index + n];	// neighbor below
 
-			fData[index] = !fData[index];
-		}
+		fData[index] = !fData[index];
+	}
 }
 
 bool Grid::ValueAt(int8 x, int8 y)

src/Grid.h

@@ -27,7 +27,7 @@ class Grid
 
 private:
 	int8 fDimension;
-	grid fData, fGrid;
+	grid fData;
 };
 
 #endif

src/Makefile

@@ -29,7 +29,7 @@ APP_MIME_SIG = application/x-vnd.wgp-LightsOff
 #	same name (source.c or source.cpp) are included from different directories.
 #	Also note that spaces in folder names do not work well with this Makefile.
 SRCS =	AboutWindow.cpp App.cpp Grid.cpp GridView.cpp MainWindow.cpp \
-		Preferences.cpp PuzzlePack.cpp TwoStateDrawButton.cpp
+		Preferences.cpp PuzzlePack.cpp TwoStateDrawButton.cpp Random.cpp
 
 #	Specify the resource definition files to use. Full or relative paths can be
 #	used.

src/Random.cpp

@@ -0,0 +1,46 @@
+/*
+ * Copyright 2018 Haiku, Inc.
+ * Distributed under the terms of the MIT License.
+ *
+ * Author:
+ *			Owen Pan <owen.pan@yahoo.com>
+ */
+
+#include "Random.h"
+
+//#define NDEBUG
+#include <assert.h>	// assert
+
+#include <stdlib.h>	// random
+
+
+static void
+Swap(int& a, int& b)
+{
+	assert (a != b);
+
+	const int tmp = a;
+	a = b;
+	b = tmp;
+}
+
+
+// array size >= n
+int ChooseRandom(int array[], int n, int k)
+{
+	assert(k > 0 && k < n);
+
+	const bool chooseComplement = n / k < 2;
+
+	if (chooseComplement)
+		k = n - k;
+
+	for (int i = 0; i < k; i++) {
+		const int offset = random() % (n - i);
+
+		if (offset > 0)
+			Swap(array[i], array[i + offset]);
+	}
+
+	return chooseComplement ? k : 0;
+}

src/Random.h

@@ -0,0 +1,6 @@
+#ifndef RANDOM_H
+#define RANDOM_H
+
+int ChooseRandom(int array[], int n, int k);
+
+#endif