added comments

Author: Ram swaroop

src/me/ramswaroop/backtracking/KnightTour.java

@@ -11,12 +11,15 @@
  * @date: 10/15/15
  * @time: 11:56 PM
  * @see: https://en.wikipedia.org/wiki/Knight%27s_tour
+ * @see: me.ramswaroop.backtracking.RatInAMaze for a simpler version of this problem
  */
 public class KnightTour {
 
     /**
-     * @param i
-     * @param j
+     * Determines if a move is a valid move in the given chess board.
+     *
+     * @param i    is the row of the new move
+     * @param j    is the column of the new move
      * @param tour
      * @return
      */
@@ -29,6 +32,9 @@ public static boolean isValidMove(int i, int j, int[][] tour) {
     }
 
     /**
+     * Finds a valid knight's tour for a given chess board size if any
+     * with the use of backtracking.
+     *
      * @param i
      * @param j
      * @param xMoves
@@ -44,35 +50,45 @@ public static boolean isValidKnightTour(int i, int j, int[] xMoves, int[] yMoves
         int nextI, nextJ;
 
         for (int k = 0; k < xMoves.length; k++) {
+            // next move is calculated from all possible moves
             nextI = i + xMoves[k];
             nextJ = j + yMoves[k];
 
+            // if the next move is valid then we proceed otherwise we 
+            // try next set of moves
             if (isValidMove(nextI, nextJ, tour)) {
                 tour[nextI][nextJ] = step;
                 if (isValidKnightTour(nextI, nextJ, xMoves, yMoves, step + 1, tour)) {
                     return true;
                 } else {
-                    tour[nextI][nextJ] = 0;
+                    tour[nextI][nextJ] = 0; // backtrack
                 }
             }
         }
 
         return false;
     }
 
+
     /**
-     * @param boardSize
+     * Prints the knight's tour if any.
+     *
+     * @param i         is the start row
+     * @param j         is the start column
+     * @param boardSize is the size of the chess board
      */
-    public static void printKnightTour(int[] boardSize) {
+    public static void printKnightTour(int i, int j, int[] boardSize) {
         if (boardSize.length < 2) return;
 
+        // a 2D array for the knight's tour
         int[][] tour = new int[boardSize[0]][boardSize[1]];
+        // all possible relative moves that a knight can make
         int[] xMoves = new int[]{1, 1, 2, 2, -1, -1, -2, -2};
         int[] yMoves = new int[]{-2, 2, -1, 1, -2, 2, -1, 1};
 
         tour[0][0] = 1;
 
-        if (isValidKnightTour(0, 0, xMoves, yMoves, 2, tour)) {
+        if (isValidKnightTour(i, j, xMoves, yMoves, 2, tour)) {
             print2DMatrix(tour);
         } else {
             System.out.println("Knight's tour doesn't exist for board size [" + boardSize[0] + "x" + boardSize[1] + "]");
@@ -90,6 +106,6 @@ public static void print2DMatrix(int[][] array) {
     }
 
     public static void main(String a[]) {
-        printKnightTour(new int[]{8, 8});
+        printKnightTour(0, 0, new int[]{8, 8});
     }
 }