pass 909 bfs medium

909-240525-pass/main.py

@@ -0,0 +1,46 @@
+class Solution:
+    def snakesAndLadders(self, board: List[List[int]]) -> int:
+        ans = 0
+        n = len(board)
+        n = n - 1
+        length = n + 1
+        que = [(1,0)]
+        idx = 0
+        flag = [0 for i in range((n+1)*(n+1))]
+        def add_node(que, idx, node):
+            if len(que) <= idx:
+                que.append(node)
+            else:
+                que[idx] = node
+        def move(idx):
+            row = 0
+            column = idx % (n + 1)
+            if idx % (n + 1) == 0: row -= 1
+            row += idx // (n + 1)
+            row = n - row
+            oe = idx // (n + 1) % 2
+            if idx % (n + 1) == 0: oe = 1 - oe
+            if column == 0: column = n + 1
+            column -= 1
+            if oe == 1: column = n - column
+            return (row, column)
+        front = 0
+        while idx - front >= 0:
+            node = que[front]
+            front += 1
+            step = node[1]
+            cur_loc = node[0]
+            if flag[cur_loc] == 1: continue
+            flag[cur_loc] = 1
+            if cur_loc + 6 >=  length * length:
+                return step + 1
+            for i in range(1, 7):
+                (row, column) = move(i + cur_loc)
+                if board[row][column]!= -1:
+                    if board[row][column] == length * length: return step + 1
+                    idx += 1
+                    add_node(que, idx, (board[row][column], step + 1))
+                else:
+                    idx += 1
+                    add_node(que, idx, (i + cur_loc, step + 1))
+        return -1