May 31

Author: siddydutta

2025-05-May-LeetCoding-Challenge/README.md

@@ -34,12 +34,12 @@
 | May 28 | [3372. Maximize the Number of Target Nodes After Connecting Trees I](https://leetcode.com/problems/maximize-the-number-of-target-nodes-after-connecting-trees-i/) | Medium | Solved |
 | May 29 | [3373. Maximize the Number of Target Nodes After Connecting Trees II](https://leetcode.com/problems/maximize-the-number-of-target-nodes-after-connecting-trees-ii/) | Hard | Unsolved |
 | May 30 | [2359. Find Closest Node to Given Two Nodes](https://leetcode.com/problems/find-closest-node-to-given-two-nodes/) | Medium | Solved |
-| May 31 | []() |  |  |
+| May 31 | [909. Snakes and Ladders](https://leetcode.com/problems/snakes-and-ladders/) | Medium | Solved |
 
 
 ## Summary
 | Level  | Problems | Solved | Unsolved |
 | ---    | --- | --- | --- |
 | Easy   | 7 | 7 | 0 |
-| Medium | 15 | 12 | 3 |
+| Medium | 16 | 13 | 3 |
 | Hard   | 7 | 1 | 6 |

2025-05-May-LeetCoding-Challenge/Snakes and Ladders.py

@@ -0,0 +1,51 @@
+from collections import deque
+
+
+class Solution:
+    def __init__(self):
+        self.n = 0
+
+    def __get_coordinates(self, position: int) -> tuple[int, int]:
+        row = (position - 1) // self.n
+        col = (position - 1) % self.n
+        if row % 2 == 1:
+            col = self.n - 1 - col
+        return self.n - 1 - row, col
+
+    def snakesAndLadders(self, board: list[list[int]]) -> int:
+        self.n = len(board)
+        queue = deque([(1, 0)])  # (position, moves)
+        visited = {1}
+        while queue:
+            position, moves = queue.popleft()
+            if position == self.n * self.n:
+                return moves
+            for move in range(1, 7):
+                new_position = position + move
+                if new_position > self.n * self.n:
+                    continue
+                row, col = self.__get_coordinates(new_position)
+                if board[row][col] != -1:
+                    new_position = board[row][col]
+                if new_position not in visited:
+                    queue.append((new_position, moves + 1))
+                    visited.add(new_position)
+        return -1
+
+
+def main():
+    board = [[-1, -1, -1, -1, -1, -1],
+             [-1, -1, -1, -1, -1, -1],
+             [-1, -1, -1, -1, -1, -1],
+             [-1, 35, -1, -1, 13, -1],
+             [-1, -1, -1, -1, -1, -1],
+             [-1, 15, -1, -1, -1, -1]]
+    assert Solution().snakesAndLadders(board) == 4
+
+    board = [[-1, -1],
+             [-1, 3]]
+    assert Solution().snakesAndLadders(board) == 1
+
+
+if __name__ == '__main__':
+    main()