1116 Print Zero Even Odd.py

Author: rajeevranjancom

1116 Print Zero Even Odd.py

@@ -0,0 +1,95 @@
+#!/usr/bin/python3
+"""
+uppose you are given the following code:
+
+class ZeroEvenOdd {
+  public ZeroEvenOdd(int n) { ... }      // constructor
+  public void zero(printNumber) { ... }  // only output 0's
+  public void even(printNumber) { ... }  // only output even numbers
+  public void odd(printNumber) { ... }   // only output odd numbers
+}
+The same instance of ZeroEvenOdd will be passed to three different threads:
+
+Thread A will call zero() which should only output 0's.
+Thread B will call even() which should only ouput even numbers.
+Thread C will call odd() which should only output odd numbers.
+Each of the threads is given a printNumber method to output an integer. Modify
+the given program to output the series 010203040506... where the length of the
+series must be 2n.
+
+
+Example 1:
+
+Input: n = 2
+Output: "0102"
+Explanation: There are three threads being fired asynchronously. One of them
+calls zero(), the other calls even(), and the last one calls odd(). "0102" is
+the correct output.
+Example 2:
+
+Input: n = 5
+Output: "0102030405"
+"""
+from typing import Callable
+from threading import Lock
+
+
+class ZeroEvenOdd:
+    def __init__(self, n):
+        """
+        only use 3 locks, and zero() knows and commonds which lock to release,
+        determing whether even() or odd() will run.
+        """
+        self.n = n
+        self.locks = [Lock() for _ in range(3)]
+        self.locks[1].acquire()
+        self.locks[2].acquire()
+
+	# printNumber(x) outputs "x", where x is an integer.
+    def zero(self, printNumber: Callable[[int], None]) -> None:
+        for i in range(self.n):
+            self.locks[0].acquire()
+            printNumber(0)
+            if (i + 1) % 2 == 1:
+                self.locks[1].release()
+            else:
+                self.locks[2].release()
+
+    def odd(self, printNumber: Callable[[int], None]) -> None:
+        for i in range((self.n + 1) // 2):
+            self.locks[1].acquire()
+            printNumber(i * 2 + 1)
+            self.locks[0].release()
+
+    def even(self, printNumber: Callable[[int], None]) -> None:
+        for i in range(self.n // 2):
+            self.locks[2].acquire()
+            printNumber(i * 2 + 2)
+            self.locks[0].release()
+
+
+class ZeroEvenOddError:
+    def __init__(self, n):
+        """
+        Like 1115, two layer of locks can do: zero and non-zero alternating,
+        odd and even alternating. 4 locks required.
+
+        Using only 3 locks?
+        """
+        self.n = n
+        self.locks = [Lock(), Lock(), Lock(), Lock()]
+        for i in range(1, len(self.locks)):
+            self.locks[i].acquire()
+
+	# printNumber(x) outputs "x", where x is an integer.
+    def zero(self, printNumber: 'Callable[[int], None]') -> None:
+        with self.locks[0]:
+            printNumber(0)
+
+    def even(self, printNumber: 'Callable[[int], None]') -> None:
+        # cannot lock self.locks[1] from both "even" and "odd"
+        pass
+
+
+    def odd(self, printNumber: 'Callable[[int], None]') -> None:
+        pass