909. Snakes and Ladders

Author: Partho Biswas

README.md

@@ -525,6 +525,7 @@ BFS, DFS, Dijkstra, Floyd–Warshall, Bellman-Ford, Kruskal, Prim's, Minimum Spa
 |29| **[947. Most Stones Removed with Same Row or Column](https://tinyurl.com/rrm6w2a)** | [Python](https://tinyurl.com/wu6rdaw/947_Most_Stones_Removed_with_Same_Row_or_Column.py), [Swift](https://tinyurl.com/wuja3c4/947_Most_Stones_Removed_with_Same_Row_or_Column.swift) | [Vid 1](https://tinyurl.com/sc2g6eg), [Art 1](https://tinyurl.com/sxyzxkr), [Vid 2](https://tinyurl.com/wocnrhn), [Art 2](https://tinyurl.com/sogsj74), [Art 3](https://tinyurl.com/w4pk463) | Medium |📌 DFS and Union FInd |
 |30| [1042. Flower Planting With No Adjacent](https://tinyurl.com/unwlzyy) | [Python](https://tinyurl.com/wu6rdaw/1042_Flower_Planting_With_No_Adjacent.py), [Swift](https://tinyurl.com/wuja3c4/1042_Flower_Planting_With_No_Adjacent.swift) | --- | Easy |📌 Could be done using DFS, BFS |
 |31| **[994_Rotting_Oranges](https://tinyurl.com/yavrnvu5)** | [Python](https://tinyurl.com/wu6rdaw/994_Rotting_Oranges.py), [Swift](https://tinyurl.com/wuja3c4/994_Rotting_Oranges.swift) | --- | Medium |📌 BFS |
+|32| **[909. Snakes and Ladders](https://tinyurl.com/yazkm38f)** | [Python](https://tinyurl.com/wu6rdaw/909_Snakes_and_Ladders.py), [Swift](https://tinyurl.com/wuja3c4/909_Snakes_and_Ladders.swift) | [Art 1](https://tinyurl.com/ya45spcc), [Art 2](https://tinyurl.com/ycafdfr4), [Art 3](https://tinyurl.com/yc3hdaw9), [Vid 1](https://tinyurl.com/yc3hdaw9), [Vid 2](https://tinyurl.com/y99hrfvk), | Medium |📌 BFS |
 
 
 </p>

leetcode.com/python/909_Snakes_and_Ladders.py

@@ -0,0 +1,51 @@
+"""
+[
+[-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]]
+
+[
+[4,-1],
+[-1,3]]
+
+9, 6
+1, 3
+
+
+6-1-3
+"""
+
+
+class Solution(object):
+    def snakesAndLadders(self, board):
+        """
+        :type board: List[List[int]]
+        :rtype: int
+        """
+        rowCount = len(board)
+        seen = set()
+        queue = collections.deque()
+        queue.append((1, 0))  # label, step
+        while queue:
+            label, step = queue.popleft()
+            r, c = self.labelToPosition(label, rowCount)
+            if board[r][c] != -1:
+                label = board[r][c]
+            if label == rowCount * rowCount:  # we have reached to our destination
+                return step
+            for nextMove in range(1, 7):
+                newLabel = label + nextMove
+                if newLabel <= rowCount * rowCount and newLabel not in seen:
+                    seen.add(newLabel)
+                    queue.append((newLabel, step + 1))
+        return -1
+
+    def labelToPosition(self, label, rowCount):
+        r, c = divmod(label - 1, rowCount)
+        if r % 2 == 0:  # even number of row
+            return rowCount - 1 - r, c
+        else:  # odd number of row
+            return rowCount - 1 - r, rowCount - 1 - c