Add Maze exercise and solution

src/main/java/com/packt/datastructuresandalg/lesson6/activity/maze/Maze.java

@@ -0,0 +1,43 @@
+package com.packt.datastructuresandalg.lesson6.activity.maze;
+
+public class Maze {
+    private int H;
+    private int W;
+    private int exitI;
+    private int exitJ;
+    private String[] maze;
+
+    public Maze(String[] maze) {
+        this.maze = maze;
+        this.H = maze.length;
+        this.W = maze[0].length();
+        for (int i = 0; i < W; i++) {
+            if (maze[0].charAt(i) == '.') {
+                this.exitI = 0;
+                this.exitJ = i;
+                return;
+            }
+            if (maze[H - 1].charAt(i) == '.') {
+                this.exitI = H - 1;
+                this.exitJ = i;
+                return;
+            }
+        }
+        for (int i = 1; i < H - 1; i++) {
+            if (maze[i].charAt(0) == '.') {
+                this.exitI = i;
+                this.exitJ = 0;
+                return;
+            }
+            if (maze[i].charAt(W - 1) == '.') {
+                this.exitI = i;
+                this.exitJ = W - 1;
+                return;
+            }
+        }
+    }
+
+    public int distToExit(int i, int j) {
+        return -1;
+    }
+}

src/main/java/com/packt/datastructuresandalg/lesson6/activity/maze/solution/Maze.java

@@ -0,0 +1,80 @@
+package com.packt.datastructuresandalg.lesson6.activity.maze.solution;
+
+import java.util.LinkedList;
+import java.util.Queue;
+
+public class Maze {
+    private int H;
+    private int W;
+    private int exitI;
+    private int exitJ;
+    private String[] maze;
+
+    public Maze(String[] maze) {
+        this.maze = maze;
+        this.H = maze.length;
+        this.W = maze[0].length();
+        for (int i = 0; i < W; i++) {
+            if (maze[0].charAt(i) == '.') {
+                this.exitI = 0;
+                this.exitJ = i;
+                return;
+            }
+            if (maze[H - 1].charAt(i) == '.') {
+                this.exitI = H - 1;
+                this.exitJ = i;
+                return;
+            }
+        }
+        for (int i = 1; i < H - 1; i++) {
+            if (maze[i].charAt(0) == '.') {
+                this.exitI = i;
+                this.exitJ = 0;
+                return;
+            }
+            if (maze[i].charAt(W - 1) == '.') {
+                this.exitI = i;
+                this.exitJ = W - 1;
+                return;
+            }
+        }
+    }
+
+    private class Pos {
+        int i;
+        int j;
+        public Pos(int i, int j) {
+            this.i = i;
+            this.j = j;
+        }
+    }
+
+    public int distToExit(int i, int j) {
+        int[][] dist = new int[H][W];
+        int[][] directions = {{1, 0}, {0, 1}, {-1, 0}, {0, -1}};
+
+        for (int h = 0; h < H; h++) {
+            for (int w = 0; w < W; w++) {
+                dist[h][w] = -1;
+            }
+        }
+
+        Queue<Pos> q = new LinkedList<>();
+        dist[i][j] = 0;
+        q.add(new Pos(i, j));
+        while (!q.isEmpty()) {
+            Pos current = q.remove();
+            if (current.i == this.exitI && current.j == this.exitJ)
+                return dist[current.i][current.j];
+            for (int d = 0; d < directions.length; d++) {
+                int ni = current.i + directions[d][0];
+                int nj = current.j + directions[d][1];
+                if (this.maze[ni].charAt(nj) == '.' && dist[ni][nj] == -1) {
+                    dist[ni][nj] = dist[current.i][current.j] + 1;
+                    q.add(new Pos(ni, nj));
+                }
+            }
+        }
+        return -1;
+    }
+}

src/main/java/com/packt/datastructuresandalg/lesson6/dfs/Graph.java

@@ -0,0 +1,59 @@
+package com.packt.datastructuresandalg.lesson6.dfs;
+
+import java.util.ArrayList;
+
+public class Graph {
+    ArrayList<Integer> adj[];
+
+    public Graph(int nodes) {
+        this.adj = new ArrayList[nodes];
+        for (int i = 0; i < nodes; i++) {
+            this.adj[i] = new ArrayList<>();
+        }
+    }
+
+    public void addEdge(int u, int v) {
+        this.adj[u].add(v);
+    }
+
+    public int[] dfs() {
+        boolean[] visited = new boolean[adj.length];
+        int[] parent = new int[adj.length];
+        for (int i = 0; i < adj.length; i++) {
+            visited[i] = false;
+            parent[i] = -1;
+        }
+        for (int i = 0; i < adj.length; i++) {
+            if (!visited[i])
+                dfsVisit(i, visited, parent);
+        }
+        return parent;
+    }
+
+    public void dfsVisit(int u, boolean[] visited, int[] parent) {
+        visited[u] = true;
+        for (int i = 0; i < adj[u].size(); i++) {
+            int next = adj[u].get(i);
+            if (!visited[next]) {
+                parent[next] = u;
+                dfsVisit(next, visited, parent);
+            }
+        }
+    }
+
+    public static void main(String[] args) {
+        Graph g = new Graph(6);
+        g.addEdge(0, 1);
+        g.addEdge(0, 3);
+        g.addEdge(1, 4);
+        g.addEdge(2, 4);
+        g.addEdge(2, 5);
+        g.addEdge(3, 1);
+        g.addEdge(4, 3);
+        g.addEdge(5, 5);
+        int[] p = g.dfs();
+        for (int i = 0; i < 6; i++) {
+            System.out.println("Parent of " + i + " in DFS forest is " + p[i]);
+        }
+    }
+}

src/test/java/com/packt/datastructuresandalg/lesson6/activity/maze/MazeTest.java

@@ -0,0 +1,20 @@
+package com.packt.datastructuresandalg.lesson6.activity.maze;
+
+import junit.framework.TestCase;
+
+public class MazeTest extends TestCase {
+    public void test1() {
+        Maze m = new Maze(new String[]{
+                "####.##",
+                "#....##",
+                "#.#.#.#",
+                "#.#...#",
+                "#.###.#",
+                "#.....#",
+                "#######"
+        });
+        assertTrue(m.distToExit(1, 1) == 4);
+        assertTrue(m.distToExit(5, 1) == 8);
+        assertTrue(m.distToExit(2, 5) == 7);
+    }
+}

src/test/java/com/packt/datastructuresandalg/lesson6/activity/weightedundirected/AdjacencyMatrixWeightedUndirectedTest.java

@@ -2,9 +2,6 @@
 
 import junit.framework.TestCase;
 
-import java.util.ArrayList;
-import java.util.Arrays;
-
 public class AdjacencyMatrixWeightedUndirectedTest extends TestCase {
     public void test1() {
         AdjacencyMatrixWeightedUndirected g = new AdjacencyMatrixWeightedUndirected(5);