snake and ladder problem

Author: sherlockwayne

src/main/java/com/thealgorithms/others/SnakeAndLadder.java

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+package com.thealgorithms.others;
+
+import java.util.LinkedList;
+import java.util.Queue;
+import java.util.Scanner;
+
+public class SnakeAndLadder {
+    public static class QueueEntry {
+        //cell number
+        int cell;
+        //distance of the cell from source cell
+        int distance;
+    }
+
+    public static int getMinimumDiceThrows(int numberOfCells, int[] graph) {
+        //Array to keep track of which cells we have visited, 0 means unvisited, 1 means visited
+        int[] visited = new int[numberOfCells];
+        for (int i = 0; i < numberOfCells; i++) {
+            visited[i] = 0;
+        }
+        //Inserting the source node in queue for BFS
+        Queue<QueueEntry> queue = new LinkedList<>();
+        QueueEntry startingQueueEntry = new QueueEntry();
+        startingQueueEntry.cell = 0;
+        startingQueueEntry.distance = 0;
+        visited[0] = 1;
+        queue.add(startingQueueEntry);
+
+        //Using BFS
+        QueueEntry currentQueueEntry = null;
+        while (!queue.isEmpty()) {
+            currentQueueEntry = queue.remove();
+            //Our goal is to reach the ending cell, so we terminate the loop when it's reached
+            if (currentQueueEntry.cell == numberOfCells - 1) {
+                break;
+            }
+            for (int i = currentQueueEntry.cell + 1; i <= currentQueueEntry.cell + 6 && i < numberOfCells; i++) {
+                if (visited[i] == 0) {
+                    visited[i] = 1;
+                    QueueEntry queueEntry = new QueueEntry();
+                    queueEntry.distance = currentQueueEntry.distance + 1;
+
+                    if (graph[i] == -1) {
+                        queueEntry.cell = i;
+                    } else {
+                        queueEntry.cell = graph[i];
+                    }
+                    queue.add(queueEntry);
+                }
+            }
+        }
+        return currentQueueEntry.distance;
+    }
+
+    public static void main(String args[]) {
+        Scanner in = new Scanner(System.in);
+        System.out.println("Enter number of cells in board");
+        int numberOfCells = in.nextInt();
+
+        //Representation of the board as graph
+        //If there are no snakes or ladders starting from a cell, we mark it as -1
+        //If there is a snake or ladder, we assign the ending position of the snake and ladder
+        int[] graph = new int[numberOfCells];
+        for (int i = 0; i < numberOfCells; i++) {
+            graph[i] = -1;
+        }
+
+        System.out.println("Enter number of snakes and ladders");
+        int n = in.nextInt();
+        System.out.println("Enter starting cell and ending cell of snake or ladder");
+        int[] positions = new int[2 * n];
+        for (int i = 0; i < n; i++) {
+            int startingCell = in.nextInt();
+            int endingCell = in.nextInt();
+            positions[2 * i] = startingCell;
+            positions[2 * i + 1] = endingCell;
+            //If there is a snake or ladder, we assign the ending position of the snake and ladder
+            graph[startingCell - 1] = endingCell - 1;
+        }
+        System.out.println("Minimum number of dice throws required to end the game is " + getMinimumDiceThrows(numberOfCells, graph));
+
+    }
+}