Create Snake&LadderProblem.cpp

Snake&LadderProblem.cpp

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+// C++ program to find minimum number of dice throws required to
+// reach last cell from first cell of a given snake and ladder
+// board
+#include<iostream>
+#include <queue>
+using namespace std;
+
+// An entry in queue used in BFS
+struct queueEntry
+{
+	int v;	 // Vertex number
+	int dist; // Distance of this vertex from source
+};
+
+// This function returns minimum number of dice throws required to
+// Reach last cell from 0'th cell in a snake and ladder game.
+// move[] is an array of size N where N is no. of cells on board
+// If there is no snake or ladder from cell i, then move[i] is -1
+// Otherwise move[i] contains cell to which snake or ladder at i
+// takes to.
+int getMinDiceThrows(int move[], int N)
+{
+	// The graph has N vertices. Mark all the vertices as
+	// not visited
+	bool *visited = new bool[N];
+	for (int i = 0; i < N; i++)
+		visited[i] = false;
+
+	// Create a queue for BFS
+	queue<queueEntry> q;
+
+	// Mark the node 0 as visited and enqueue it.
+	visited[0] = true;
+	queueEntry s = {0, 0}; // distance of 0't vertex is also 0
+	q.push(s); // Enqueue 0'th vertex
+
+	// Do a BFS starting from vertex at index 0
+	queueEntry qe; // A queue entry (qe)
+	while (!q.empty())
+	{
+		qe = q.front();
+		int v = qe.v; // vertex no. of queue entry
+
+		// If front vertex is the destination vertex,
+		// we are done
+		if (v == N-1)
+			break;
+
+		// Otherwise dequeue the front vertex and enqueue
+		// its adjacent vertices (or cell numbers reachable
+		// through a dice throw)
+		q.pop();
+		for (int j=v+1; j<=(v+6) && j<N; ++j)
+		{
+			// If this cell is already visited, then ignore
+			if (!visited[j])
+			{
+				// Otherwise calculate its distance and mark it
+				// as visited
+				queueEntry a;
+				a.dist = (qe.dist + 1);
+				visited[j] = true;
+
+				// Check if there a snake or ladder at 'j'
+				// then tail of snake or top of ladder
+				// become the adjacent of 'i'
+				if (move[j] != -1)
+					a.v = move[j];
+				else
+					a.v = j;
+				q.push(a);
+			}
+		}
+	}
+
+	// We reach here when 'qe' has last vertex
+	// return the distance of vertex in 'qe'
+	return qe.dist;
+}
+
+// Driver program to test methods of graph class
+int main()
+{
+	// Let us construct the board given in above diagram
+	int N = 30;
+	int moves[N];
+	for (int i = 0; i<N; i++)
+		moves[i] = -1;
+
+	// Ladders
+	moves[2] = 21;
+	moves[4] = 7;
+	moves[10] = 25;
+	moves[19] = 28;
+
+	// Snakes
+	moves[26] = 0;
+	moves[20] = 8;
+	moves[16] = 3;
+	moves[18] = 6;
+
+	cout << "Min Dice throws required is " << getMinDiceThrows(moves, N);
+	return 0;
+}