Added comments to code

Header/NPuzzleSolver.cpp

@@ -7,6 +7,8 @@
 
 #define MAX_NO_OF_LEVELS 25
 
+
+// Constructor for NPuzzleSolver.
 NPuzzleSolver::NPuzzleSolver(const std::string &puzzle) {
 	std::stringstream ss(puzzle);
 	unsigned short n;
@@ -19,13 +21,15 @@ NPuzzleSolver::NPuzzleSolver(const std::string &puzzle) {
 }
 
 
+// Prints a line separator to split the rows of the N-puzzle on the terminal.
 void NPuzzleSolver::printSeparator(const char &ch, const unsigned short &boxWidth, const unsigned short &boardSize) {
 	for(unsigned short i = 1; i < boardSize; i++)
 		std::cout << std::string(boxWidth, ch) << "|";
 	std::cout << std::string(boxWidth, ch) << std::endl;
 }
 
 
+// Prints the N-puzzle on the terminal.
 void NPuzzleSolver::printPuzzle() const {
 	const unsigned short boxWidth = std::to_string(puzzleBoard.size()).length() + 2, boardSize = std::sqrt(puzzleBoard.size());
 	std::cout << "Board size: " << boardSize << std::endl;
@@ -53,6 +57,7 @@ void NPuzzleSolver::printPuzzle() const {
 }
 
 
+// Main method to solve the N-puzzle by adding a layer to the decision tree until either the solution is found or the MAX_NO_OF_LEVELS threshold is reached.
 void NPuzzleSolver::solve() {
 	std::string solution = "";
 	const unsigned short emptySlotIndex = distance(puzzleBoard.begin(), std::find(puzzleBoard.begin(), puzzleBoard.end(), 0)), boardSize = std::sqrt(puzzleBoard.size());

Header/NPuzzleSolver.h

@@ -5,6 +5,8 @@
 #include <string>
 #include <vector>
 
+
+// NPuzzleSolver class declaration.
 class NPuzzleSolver {
 private:
 	std::vector<unsigned short> puzzleBoard;

Header/PathNode.cpp

@@ -3,6 +3,7 @@
 #include <set>
 
 
+// An enum containing all possible directions of the movement.
 typedef enum {
 	LEFT = 'L',
 	RIGHT = 'R',
@@ -11,13 +12,15 @@ typedef enum {
 } Directions;
 
 
+// Creates a subtree connected to the current node with directions as their child nodes.
 void PathNode::createSubtree() {
 	static std::set<char> moves = {LEFT, RIGHT, UP, DOWN};
 	for(auto i = moves.begin(); i != moves.end(); i++)
 		childNodeList.emplace(*i, PathNode());
 }
 
 
+// Adds a level to the bottom of the decision tree.
 void PathNode::addLevel() {
 	if(childNodeList.empty()) {
 		createSubtree();
@@ -28,6 +31,7 @@ void PathNode::addLevel() {
 }
 
 
+// Deletes the last level at the bottom of the decision tree.
 void PathNode::clearLastLevel() {
 	if(childNodeList.begin()->second.childNodeList.empty()) {
 		childNodeList.clear();
@@ -38,11 +42,13 @@ void PathNode::clearLastLevel() {
 }
 
 
+// Deletes the whole decision tree altogether when it is called from the root, otherwise deletes the current node's whole subtree instead.
 void PathNode::clearTree() {
 	childNodeList.clear();
 }
 
 
+// Returns TRUE if the given solution path is valid, FALSE otherwise.
 bool PathNode::checkSolution(const std::string &path, const std::vector<unsigned short> &puzzleBoard) {
 	for(size_t i = 0; i < puzzleBoard.size() - 1; i++)
 		if(puzzleBoard[i] != i + 1)
@@ -52,6 +58,8 @@ bool PathNode::checkSolution(const std::string &path, const std::vector<unsigned
 }
 
 
+// A recursive, backtracking algorithm which traverses the whole decision tree to find a valid solution path for the N-puzzle.
+// Returns TRUE if such solution path exists, FALSE otherwise.
 bool PathNode::checkAllPaths(std::string &path, std::vector<unsigned short> &puzzleBoard, const unsigned short &boardSize, unsigned short &emptySlotIndex) {
 	for(auto i = childNodeList.begin(); i != childNodeList.end(); i++) {
 		unsigned short changedElementIndex;

Header/PathNode.h

@@ -6,6 +6,7 @@
 #include <vector>
 
 
+// PathNode class declaration.
 class PathNode {
 private:
 	std::map<char, PathNode> childNodeList;

main.cpp

@@ -3,39 +3,34 @@
 
 int main() {
 	NPuzzleSolver TwoToTwo("1-2-0-3");
-
-	NPuzzleSolver ThreeToThree_ez("0-1-2-4-6-3-7-5-8");
-	NPuzzleSolver ThreeToThree_avg("5-1-2-4-6-3-0-7-8");
-	NPuzzleSolver ThreeToThree_hard("1-2-0-3-6-4-5-7-8");
-	NPuzzleSolver ThreeToThree_very_hard("4-6-7-3-2-1-5-0-8");
-	NPuzzleSolver ThreeToThree_impossible("1-2-3-4-5-6-8-7-0");
-
-	NPuzzleSolver FourToFour("2-10-4-0-1-6-3-7-5-14-12-8-9-13-11-15");
-
-	NPuzzleSolver FiveToFive("1-2-4-5-10-6-7-3-14-9-0-11-12-8-15-16-17-13-18-20-21-22-23-19-24");
-
-
 	TwoToTwo.printPuzzle();
 	TwoToTwo.solve();
 
+	NPuzzleSolver ThreeToThree_ez("0-1-2-4-6-3-7-5-8");
 	ThreeToThree_ez.printPuzzle();
 	ThreeToThree_ez.solve();
 
+	NPuzzleSolver ThreeToThree_avg("5-1-2-4-6-3-0-7-8");
 	ThreeToThree_avg.printPuzzle();
 	ThreeToThree_avg.solve();
 
+	NPuzzleSolver ThreeToThree_hard("1-2-0-3-6-4-5-7-8");
 	ThreeToThree_hard.printPuzzle();
 	ThreeToThree_hard.solve();
 
+	NPuzzleSolver ThreeToThree_very_hard("4-6-7-3-2-1-5-0-8");
 	ThreeToThree_very_hard.printPuzzle();
 	ThreeToThree_very_hard.solve();
 
+	NPuzzleSolver ThreeToThree_impossible("1-2-3-4-5-6-8-7-0");
 	ThreeToThree_impossible.printPuzzle();
 	ThreeToThree_impossible.solve();
 
+	NPuzzleSolver FourToFour("2-10-4-0-1-6-3-7-5-14-12-8-9-13-11-15");
 	FourToFour.printPuzzle();
 	FourToFour.solve();
 
+	NPuzzleSolver FiveToFive("1-2-4-5-10-6-7-3-14-9-0-11-12-8-15-16-17-13-18-20-21-22-23-19-24");
 	FiveToFive.printPuzzle();
 	FiveToFive.solve();