Question No 1 Solved

Author: akashdeep023

18-Backtracking/Assignment_Backtracking.java

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+public class Assignment_Backtracking {
+    public static void ratInMaze(int maze[][], int row, int col, int newMaze[][]) {
+        // base case
+        if (row == maze.length - 1 && col == maze.length - 1) {
+            newMaze[row][col] = 1;
+            printMaze(newMaze);
+            return;
+        }
+        // recursion 
+        if (col < maze.length - 1 && maze[row][col + 1] == 1) { // right
+            newMaze[row][col] = 1;
+            ratInMaze(maze, row, col + 1, newMaze);
+            newMaze[row][col] = 0;
+        }
+        if (row < maze.length - 1 && maze[row + 1][col] == 1) { // down
+            newMaze[row][col] = 1;
+            ratInMaze(maze, row + 1, col, newMaze);
+            newMaze[row][col] = 0;
+        }
+    }
+
+    public static void printMaze(int maze[][]) {
+        for (int i = 0; i < maze.length; i++) {
+            for (int j = 0; j < maze.length; j++) {
+                System.out.print(maze[i][j] + " ");
+            }
+            System.out.println();
+        }
+        System.out.println();
+    }
+
+    public static void main(String[] args) {
+        // Question 1 : Rat in a Maze --------------------------------
+        // You are given a starting position for a rat which is stuck in a maze at an initial point (0, 0) (the
+        // maze can be thought of as a 2-dimensional plane). The maze would be given in the form of a
+        // square matrix of order N * N where the cells with value 0 represent the maze’s blocked
+        // locations while value 1 is the open/available path that the rat can take to reach its destination.
+        // The rat's destination is at (N - 1, N - 1).
+        // Your task is to find all the possible paths that the rat can take to reach from source to
+        // destination in the maze.
+        // The possible directions that it can take to move in the maze are 'U'(up) i.e. (x, y - 1) , 'D'(down)
+        // i.e. (x, y + 1) , 'L' (left) i.e. (x - 1, y), 'R' (right) i.e. (x + 1, y)
+        // (This problem is similar to Grid ways.)
+        int maze[][] = {
+                { 1, 0, 0, 0 },
+                { 1, 1, 0, 1 },
+                { 0, 1, 0, 0 },
+                { 1, 1, 1, 1 }
+        };
+        int newMaze[][] = new int[4][4];
+        ratInMaze(maze, 0, 0, newMaze);
+        // Output = 1 0 0 0
+        //          1 1 0 0
+        //          0 1 0 0
+        //          0 1 1 1
+
+        // Question 2 : Keypad Combinations --------------------------------
+        // Given a string containing digits from 2-9 inclusive, print all possible letter combinations that
+        // the number could represent. You can print the answer in any order.
+        // A mapping of digits to letters (just like on the telephone buttons) is given below. Note that 1
+        // does not map to any letters.
+        String digits1 = "23"; // Output : "ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"
+        String digits2 = "2"; // Output : "a", "b", "c"
+        String digits3 = ""; // Output : ""
+
+        // Question 3 : Knight’s Tour --------------------------------
+        // Given a N*N board with the Knight placed on the first block of an empty board. Moving
+        // according to the rules of chess, knights must visit each square exactly once. Print the order of
+        // each cell in which they are visited. (Hint : Similar to N Queens)
+        int N = 8;
+        // Output = 0 59 38 33 30 17  8 63
+        //         37 34 31 60  9 62 29 16
+        //         58  1 36 39 32 27 18  7
+        //         35 48 41 26 61 10 15 28
+        //         42 57  2 49 40 23  6 19
+        //         47 50 45 54 25 20 11 14
+        //         56 43 52  3 22 13 24  5
+        //         51 46 55 44 53  4 21 12
+
+    }
+}