#225 is completed

Author: Hamid Gasmi

09-problems/lc_957_prison_cells.py

@@ -0,0 +1,67 @@
+class Solution:
+    """
+    calls[i] = 1 if cells[i - 1] == cell[i+1]
+    cells[i] = 0
+    Approach:
+      1. Find the operation that will let me know go from day d to day d+1
+      2. loop until I get cycle or I get to N (64 possible combinations)
+      3. loop again N mod cycle
+      
+    """
+    # There're 2**6 states: 65 + 1 (the initial one)
+    # Time Analysis: O(2**6) = O(1)
+    # Space Complexity: O(1)
+    def prisonAfterNDays(self, cells: List[int], N: int) -> List[int]:
+        
+        if N == 0:
+            return cells
+
+        # 1. Convert the list to bitmap
+        cells_state = self._convert_list_bitmap(cells)
+        
+        # 2. State at Day 1
+        cells_state = self.next_state(cells_state)
+        N -= 1
+        
+        # 3. Find the cycle
+        cycle = 0
+        initial_state = cells_state
+        while N:
+            
+            N -= 1
+            cycle += 1
+            cells_state = self.next_state(cells_state)
+            if cells_state == initial_state:
+                break
+        
+        # 4. If N too small, then stop
+        if N == 0:
+            self._convert_int_to_list(cells_state, cells)
+            return cells
+        
+        # 5. loop at most cycle - 1 times
+        for _ in range(N % cycle):
+            cells_state = self.next_state(cells_state)
+        
+        # 6. Convert the bitmap to list
+        self._convert_int_to_list(cells_state, cells)
+        return cells
+        
+    def next_state(self, cells_state: int) -> int:
+        
+        return ( (~(cells_state << 1)) ^ cells_state >> 1) & 0x007e
+        
+    def _convert_list_bitmap(self, cells: List[int]) -> int:
+        
+        cells_state = 0
+        for cell in cells:
+            cells_state <<= 1
+            cells_state |= cell
+        
+        return cells_state
+    
+    def _convert_int_to_list(self, cells_state, cells: List[int]):
+                
+        for i in range(7, -1, -1):
+            cells[i] = cells_state & 1
+            cells_state >>= 1