957. Prison Cells After N Days

Author: Partho Biswas

README.md

@@ -177,6 +177,7 @@ I have solved quite a number of problems from several topics. See the below tabl
 |66| [246. Strobogrammatic Number](https://tinyurl.com/ycqwsozh) | [Python](https://tinyurl.com/wu6rdaw/246_Strobogrammatic_Number.py), [Swift](https://tinyurl.com/wuja3c4/246_Strobogrammatic_Number.swift) |  | Easy |  |
 |67| **[845. Longest Mountain in Array](https://tinyurl.com/y9h5uah5)** | [Python](https://tinyurl.com/wu6rdaw/845_Longest_Mountain_in_Array.py), [Swift](https://tinyurl.com/wuja3c4/845_Longest_Mountain_in_Array.swift) |  | Medium |  |
 |68| **[66. Plus One](https://tinyurl.com/yd67rugq)** | [Python](https://tinyurl.com/wu6rdaw/66_Plus_One.py), [Swift](https://tinyurl.com/wuja3c4/66_Plus_One.swift) |  | Easy |  |
+|69| **[957. Prison Cells After N Days](https://tinyurl.com/yag46zkm)** | [Python](https://tinyurl.com/wu6rdaw/957_Prison_Cells_After_N_Days.py), [Swift](https://tinyurl.com/wuja3c4/957_Prison_Cells_After_N_Days.swift) | [Art 1](https://tinyurl.com/y7cbf32e), [Art 2](https://tinyurl.com/yd2y66dn), [Art 3](https://tinyurl.com/yczdwnwu), [Art 4](https://tinyurl.com/y8j9b593), [Art 5](https://tinyurl.com/y6u2u42m) | Medium |  |
 
 
 </p>

leetcode.com/python/957_Prison_Cells_After_N_Days.py

@@ -0,0 +1,65 @@
+"""
+{
+'[0, 1, 0, 0, 0, 1, 0, 0]': 1000000001, ----
+'[0, 1, 0, 1, 0, 0, 1, 0]': 999999992,
+'[0, 0, 1, 1, 1, 0, 0, 0]': 15,
+'[0, 1, 0, 0, 1, 1, 1, 0]': 1000000000,
+'[0, 0, 0, 1, 1, 1, 0, 0]': 999999997,
+'[0, 1, 0, 0, 1, 0, 1, 0]': 999999999,
+'[0, 0, 1, 0, 1, 0, 1, 0]': 999999995,
+'[0, 1, 0, 1, 0, 1, 0, 0]': 13,
+'[0, 1, 1, 1, 0, 0, 1, 0]': 999999993,
+'[0, 0, 1, 0, 0, 0, 1, 0]': 999999994,
+'[0, 1, 0, 0, 1, 0, 0, 0]': 999999998,
+'[0, 0, 1, 1, 1, 1, 1, 0]': 999999996, ------
+'[0, 1, 1, 1, 1, 1, 0, 0]': 14,
+'[0, 0, 0, 1, 0, 0, 1, 0]': 999999991}
+
+"""
+# My initial code. 248 / 258 test cases passed.
+# Forward calculations
+class Solution(object):
+    def prisonAfterNDays(self, cells, N):
+        """
+        :type cells: List[int]
+        :type N: int
+        :rtype: List[int]
+        """
+        seen = {}
+        lastSeenCells = []
+        currentDay = 0
+        while currentDay < N:
+            cells = [0] + [cells[i - 1] ^ cells[i + 1] ^ 1 for i in range(1, 7)] + [0]
+            key = str(cells)
+            if key in seen:
+                div, mod = divmod(N, currentDay)
+                currentDay = N - mod
+            currentDay += 1
+            seen[key] = currentDay
+            lastSeenCells = cells
+        print(seen)
+        return lastSeenCells
+
+    def prisonAfterNDays(self, cells, N):
+        seen = {str(cells): N}
+        while N:
+            seen.setdefault(str(cells), N)
+            N -= 1
+            cells = [0] + [cells[i - 1] ^ cells[i + 1] ^ 1 for i in range(1, 7)] + [0]
+            if str(cells) in seen:
+                N %= seen[str(cells)] - N
+        return cells
+
+
+# https://tinyurl.com/yczdwnwu
+# Backword calculations
+class Solution(object):
+    def prisonAfterNDays(self, cells, N):
+        seen = {str(cells): N}
+        while N:
+            seen.setdefault(str(cells), N)
+            N -= 1
+            cells = [0] + [cells[i - 1] ^ cells[i + 1] ^ 1 for i in range(1, 7)] + [0]
+            if str(cells) in seen:
+                N %= seen[str(cells)] - N
+        return cells