From d63813e0a2b05ffa3bc5d359b9b206b03e6ba962 Mon Sep 17 00:00:00 2001 From: Ong Lip Wei <57990488+hahaong@users.noreply.github.com> Date: Tue, 9 Aug 2022 01:47:04 +0800 Subject: [PATCH] Add maze recursion algorithm (#3204) --- .../backtracking/MazeRecursion.java | 158 ++++++++++++++++++ .../backtracking/MazeRecursionTest.java | 78 +++++++++ 2 files changed, 236 insertions(+) create mode 100644 src/main/java/com/thealgorithms/backtracking/MazeRecursion.java create mode 100644 src/test/java/com/thealgorithms/backtracking/MazeRecursionTest.java diff --git a/src/main/java/com/thealgorithms/backtracking/MazeRecursion.java b/src/main/java/com/thealgorithms/backtracking/MazeRecursion.java new file mode 100644 index 00000000..c52a4e6f --- /dev/null +++ b/src/main/java/com/thealgorithms/backtracking/MazeRecursion.java @@ -0,0 +1,158 @@ +package com.thealgorithms.backtracking; + +public class MazeRecursion { + + public static void mazeRecursion() { + // First create a 2 dimensions array to mimic a maze map + int[][] map = new int[8][7]; + int[][] map2 = new int[8][7]; + + // We use 1 to indicate wall + // Set the ceiling and floor to 1 + for (int i = 0; i < 7; i++) { + map[0][i] = 1; + map[7][i] = 1; + } + + // Then we set the left and right wall to 1 + for (int i = 0; i < 8; i++) { + map[i][0] = 1; + map[i][6] = 1; + } + + // Now we have created a maze with its wall initialized + + // Here we set the obstacle + map[3][1] = 1; + map[3][2] = 1; + + // Print the current map + System.out.println("The condition of the map： "); + for (int i = 0; i < 8; i++) { + for (int j = 0; j < 7; j++) { + System.out.print(map[i][j] + " "); + } + System.out.println(); + } + + // clone another map for setWay2 method + for (int i = 0; i < map.length; i++) { + for (int j = 0; j < map[i].length; j++) { + map2[i][j] = map[i][j]; + } + } + + // By using recursive backtracking to let your ball(target) find its way in the + // maze + // The first parameter is the map + // Second parameter is x coordinate of your target + // Thrid parameter is the y coordinate of your target + setWay(map, 1, 1); + setWay2(map2, 1, 1); + + // Print out the new map1, with the ball footprint + System.out.println("After the ball goes through the map1，show the current map1 condition"); + for (int i = 0; i < 8; i++) { + for (int j = 0; j < 7; j++) { + System.out.print(map[i][j] + " "); + } + System.out.println(); + } + + // Print out the new map2, with the ball footprint + System.out.println("After the ball goes through the map2，show the current map2 condition"); + for (int i = 0; i < 8; i++) { + for (int j = 0; j < 7; j++) { + System.out.print(map2[i][j] + " "); + } + System.out.println(); + } + } + + + + // Using recursive path finding to help the ball find its way in the maze + // Description： + // 1. map (means the maze) + // 2. i, j (means the initial coordinate of the ball in the maze) + // 3. if the ball can reach the end of maze, that is position of map[6][5], + // means the we have found a path for the ball + // 4. Additional Information： 0 in the map[i][j] means the ball has not gone + // through this position, 1 means the wall, 2 means the path is feasible, 3 + // means the ball has gone through the path but this path is dead end + // 5. We will need strategy for the ball to pass through the maze for example: + // Down -> Right -> Up -> Left, if the path doesn't work, then backtrack + /** + * + * @Description + * @author OngLipWei + * @date Jun 23, 202111:36:14 AM + * @param map The maze + * @param i x coordinate of your ball(target) + * @param j y coordinate of your ball(target) + * @return If we did find a path for the ball，return true，else false + */ + public static boolean setWay(int[][] map, int i, int j) { + if (map[6][5] == 2) {// means the ball find its path, ending condition + return true; + } + if (map[i][j] == 0) { // if the ball haven't gone through this point + // then the ball follows the move strategy : down -> right -> up -> left + map[i][j] = 2; // we assume that this path is feasible first, set the current point to 2 first。 + if (setWay(map, i + 1, j)) { // go down + return true; + } else if (setWay(map, i, j + 1)) { // go right + return true; + } else if (setWay(map, i - 1, j)) { // go up + return true; + } else if (setWay(map, i, j - 1)) { // go left + return true; + } else { + // means that the current point is the dead end, the ball cannot proceed, set + // the current point to 3 and return false, the backtraking will start, it will + // go to the previous step and check for feasible path again + map[i][j] = 3; + return false; + } + + } else { // if the map[i][j] != 0 , it will probably be 1,2,3, return false because the + // ball cannot hit the wall, cannot go to the path that has gone though before, + // and cannot head to deadend. + return false; + } + + } + + // Here is another move strategy for the ball: up->right->down->left + public static boolean setWay2(int[][] map, int i, int j) { + if (map[6][5] == 2) {// means the ball find its path, ending condition + return true; + } + if (map[i][j] == 0) { // if the ball haven't gone through this point + // then the ball follows the move strategy : up->right->down->left + map[i][j] = 2; // we assume that this path is feasible first, set the current point to 2 first。 + if (setWay2(map, i - 1, j)) { // go up + return true; + } else if (setWay2(map, i, j + 1)) { // go right + return true; + } else if (setWay2(map, i + 1, j)) { // go down + return true; + } else if (setWay2(map, i, j - 1)) { // go left + return true; + } else { + // means that the current point is the dead end, the ball cannot proceed, set + // the current point to 3 and return false, the backtraking will start, it will + // go to the previous step and check for feasible path again + map[i][j] = 3; + return false; + } + + } else { // if the map[i][j] != 0 , it will probably be 1,2,3, return false because the + // ball cannot hit the wall, cannot go to the path that has gone though before, + // and cannot head to deadend. + return false; + } + + } + +} diff --git a/src/test/java/com/thealgorithms/backtracking/MazeRecursionTest.java b/src/test/java/com/thealgorithms/backtracking/MazeRecursionTest.java new file mode 100644 index 00000000..a6beb209 --- /dev/null +++ b/src/test/java/com/thealgorithms/backtracking/MazeRecursionTest.java @@ -0,0 +1,78 @@ +package com.thealgorithms.backtracking; + +import org.junit.jupiter.api.Test; +import static org.junit.jupiter.api.Assertions.*; + +/** + * @author onglipwei + * @create 2022-08-03 5:17 AM + */ +public class MazeRecursionTest { + + @Test + public void testMaze() { + + + // First create a 2 dimensions array to mimic a maze map + int[][] map = new int[8][7]; + int[][] map2 = new int[8][7]; + + // We use 1 to indicate wall + // Set the ceiling and floor to 1 + for (int i = 0; i < 7; i++) { + map[0][i] = 1; + map[7][i] = 1; + } + + // Then we set the left and right wall to 1 + for (int i = 0; i < 8; i++) { + map[i][0] = 1; + map[i][6] = 1; + + } + + // Now we have created a maze with its wall initialized + + // Here we set the obstacle + map[3][1] = 1; + map[3][2] = 1; + + //clone another map for setWay2 method + for (int i = 0; i < map.length;i++) { + for (int j = 0; j < map[i].length;j++) { + map2[i][j]=map[i][j]; + } + } + + MazeRecursion.setWay(map, 1, 1); + MazeRecursion.setWay2(map2, 1, 1); + + + int expectedMap[][] = new int[][]{ + {1,1,1,1,1,1,1}, + {1,2,0,0,0,0,1}, + {1,2,2,2,0,0,1}, + {1,1,1,2,0,0,1}, + {1,0,0,2,0,0,1}, + {1,0,0,2,0,0,1}, + {1,0,0,2,2,2,1}, + {1,1,1,1,1,1,1} + }; + + int expectedMap2[][] = new int[][]{ + {1,1,1,1,1,1,1}, + {1,2,2,2,2,2,1}, + {1,0,0,0,0,2,1}, + {1,1,1,0,0,2,1}, + {1,0,0,0,0,2,1}, + {1,0,0,0,0,2,1}, + {1,0,0,0,0,2,1}, + {1,1,1,1,1,1,1} + }; + + assertArrayEquals(map, expectedMap); + assertArrayEquals(map2, expectedMap2); + + } + +}