Create random-flip-matrix.py

Author: kamyu104

Python/random-flip-matrix.py

@@ -0,0 +1,76 @@
+# Time:  O(1)
+# Space: O(min(f, r * c))
+
+# You are given the number of rows n_rows and
+# number of columns n_cols of a 2D binary matrix
+# where all values are initially 0.
+# Write a function flip which chooses a 0 value uniformly at random,
+# changes it to 1, and then returns the position [row.id, col.id] of
+# that value. Also, write a function reset which sets all values back to 0.
+# Try to minimize the number of calls to system's Math.random()
+# and optimize the time and space complexity.
+#
+# Note:
+# - 1 <= n_rows, n_cols <= 10000
+# - 0 <= row.id < n_rows and 0 <= col.id < n_cols
+# - flip will not be called when the matrix has no 0 values left.
+# - the total number of calls to flip and reset will not exceed 1000.
+# Example 1:
+#
+# Input: 
+# ["Solution","flip","flip","flip","flip"]
+# [[2,3],[],[],[],[]]
+# Output: [null,[0,1],[1,2],[1,0],[1,1]]
+# Example 2:
+#
+# Input: 
+# ["Solution","flip","flip","reset","flip"]
+# [[1,2],[],[],[],[]]
+# Output: [null,[0,0],[0,1],null,[0,0]]
+# Explanation of Input Syntax:
+#
+# The input is two lists:
+# the subroutines called and their arguments.
+# Solution's constructor has two arguments, n_rows and n_cols.
+# flip and reset have no arguments.
+# Arguments are always wrapped with a list, even if there aren't any.
+
+import random
+
+
+class Solution(object):
+
+    def __init__(self, n_rows, n_cols):
+        """
+        :type n_rows: int
+        :type n_cols: int
+        """
+        self.__n_rows = n_rows
+        self.__n_cols = n_cols
+        self.__n = n_rows*n_cols
+        self.__lookup = {}
+        
+
+    def flip(self):
+        """
+        :rtype: List[int]
+        """
+        self.__n -= 1
+        target = random.randint(0, self.__n)
+        x = self.__lookup.get(target, target)
+        self.__lookup[target] = self.__lookup.get(self.__n, self.__n)
+        return divmod(x, self.__n_cols)
+        
+
+    def reset(self):
+        """
+        :rtype: void
+        """
+        self.__n = self.__n_rows*self.__n_cols
+        self.__lookup = {}
+        
+
+# Your Solution object will be instantiated and called as such:
+# obj = Solution(n_rows, n_cols)
+# param_1 = obj.flip()
+# obj.reset()