Add Cpp solution to problem 909 (snakes and ladders)

Author: AndresLopezEsquivel

cpp/0909-snakes-and-ladders.cpp

@@ -0,0 +1,63 @@
+class Solution {
+  public:
+      // Function to get the row and column index of a position on the board
+      std::pair<int, int> get_indexes_of(int pos, std::vector<std::vector<int>>& grid)
+      {
+          int grid_w = grid.front().size();
+          int grid_h = grid.size();
+          int r = (pos - 1) / grid_w;
+          int c = (pos - 1) % grid_w;
+          // Adjust column index for alternating rows
+          c = r % 2 == 0 ? c : grid_w - (c + 1);
+          // Adjust row index to start from the bottom of the grid
+          r = grid_h - (r + 1);
+          return std::make_pair(r, c);
+      }
+
+      // Function to find the minimum number of moves to reach the last cell in Snakes and Ladders
+      // using BFS (Breadth-First Search).
+      // BFS lets us find the shortest path in an unweighted graph.
+      int snakesAndLadders(std::vector<std::vector<int>>& board)
+      {
+          int board_h = board.size();
+          int board_w = board.front().size();
+          std::vector<bool> visited((board_h * board_w) + 1, false);
+          std::vector<int> dist((board_h * board_w) + 1, -1);
+          std::deque<int> q;
+          q.push_back(1);
+          visited[1] = true;
+          dist[1] = 0;
+
+          while (!q.empty())
+          {
+              int curr_pos = q.front();
+              q.pop_front();
+
+              // If we reach the last cell, return the distance
+              if (curr_pos == board_h * board_w) return dist[board_h * board_w];
+
+              // Check the next 6 possible moves
+              for (size_t i = 1; i <= 6; ++i)
+              {
+              int next_pos = curr_pos + i;
+              if (next_pos > board_h * board_w) continue;
+
+              std::pair<int, int> next_idx = get_indexes_of(next_pos, board);
+              // If there's a snake or ladder, move to the destination cell
+              if (board[next_idx.first][next_idx.second] != -1)
+                  next_pos = board[next_idx.first][next_idx.second];
+
+              // If the next position is not visited, mark it and update the distance
+              if (!visited[next_pos])
+              {
+                  visited[next_pos] = true;
+                  q.push_back(next_pos);
+                  // dist[next_pos] indicates the number of minimum moves to reach the next position
+                  dist[next_pos] = dist[curr_pos] + 1;
+              }
+              }
+          }
+          // If we can't reach the last cell, return -1
+          return -1;
+      }
+  };