|
| 1 | +#!/usr/bin/python3 |
| 2 | +""" |
| 3 | +uppose you are given the following code: |
| 4 | +
|
| 5 | +class ZeroEvenOdd { |
| 6 | + public ZeroEvenOdd(int n) { ... } // constructor |
| 7 | + public void zero(printNumber) { ... } // only output 0's |
| 8 | + public void even(printNumber) { ... } // only output even numbers |
| 9 | + public void odd(printNumber) { ... } // only output odd numbers |
| 10 | +} |
| 11 | +The same instance of ZeroEvenOdd will be passed to three different threads: |
| 12 | +
|
| 13 | +Thread A will call zero() which should only output 0's. |
| 14 | +Thread B will call even() which should only ouput even numbers. |
| 15 | +Thread C will call odd() which should only output odd numbers. |
| 16 | +Each of the threads is given a printNumber method to output an integer. Modify |
| 17 | +the given program to output the series 010203040506... where the length of the |
| 18 | +series must be 2n. |
| 19 | +
|
| 20 | +
|
| 21 | +Example 1: |
| 22 | +
|
| 23 | +Input: n = 2 |
| 24 | +Output: "0102" |
| 25 | +Explanation: There are three threads being fired asynchronously. One of them |
| 26 | +calls zero(), the other calls even(), and the last one calls odd(). "0102" is |
| 27 | +the correct output. |
| 28 | +Example 2: |
| 29 | +
|
| 30 | +Input: n = 5 |
| 31 | +Output: "0102030405" |
| 32 | +""" |
| 33 | +fromtypingimportCallable |
| 34 | +fromthreadingimportLock |
| 35 | + |
| 36 | + |
| 37 | +classZeroEvenOdd: |
| 38 | +def__init__(self,n): |
| 39 | +""" |
| 40 | + only use 3 locks, and zero() knows and commonds which lock to release, |
| 41 | + determing whether even() or odd() will run. |
| 42 | + """ |
| 43 | +self.n=n |
| 44 | +self.locks= [Lock()for_inrange(3)] |
| 45 | +self.locks[1].acquire() |
| 46 | +self.locks[2].acquire() |
| 47 | + |
| 48 | +# printNumber(x) outputs "x", where x is an integer. |
| 49 | +defzero(self,printNumber:Callable[[int],None])->None: |
| 50 | +foriinrange(self.n): |
| 51 | +self.locks[0].acquire() |
| 52 | +printNumber(0) |
| 53 | +if (i+1)%2==1: |
| 54 | +self.locks[1].release() |
| 55 | +else: |
| 56 | +self.locks[2].release() |
| 57 | + |
| 58 | +defodd(self,printNumber:Callable[[int],None])->None: |
| 59 | +foriinrange((self.n+1)//2): |
| 60 | +self.locks[1].acquire() |
| 61 | +printNumber(i*2+1) |
| 62 | +self.locks[0].release() |
| 63 | + |
| 64 | +defeven(self,printNumber:Callable[[int],None])->None: |
| 65 | +foriinrange(self.n//2): |
| 66 | +self.locks[2].acquire() |
| 67 | +printNumber(i*2+2) |
| 68 | +self.locks[0].release() |
| 69 | + |
| 70 | + |
| 71 | +classZeroEvenOddError: |
| 72 | +def__init__(self,n): |
| 73 | +""" |
| 74 | + Like 1115, two layer of locks can do: zero and non-zero alternating, |
| 75 | + odd and even alternating. 4 locks required. |
| 76 | +
|
| 77 | + Using only 3 locks? |
| 78 | + """ |
| 79 | +self.n=n |
| 80 | +self.locks= [Lock(),Lock(),Lock(),Lock()] |
| 81 | +foriinrange(1,len(self.locks)): |
| 82 | +self.locks[i].acquire() |
| 83 | + |
| 84 | +# printNumber(x) outputs "x", where x is an integer. |
| 85 | +defzero(self,printNumber:'Callable[[int], None]')->None: |
| 86 | +withself.locks[0]: |
| 87 | +printNumber(0) |
| 88 | + |
| 89 | +defeven(self,printNumber:'Callable[[int], None]')->None: |
| 90 | +# cannot lock self.locks[1] from both "even" and "odd" |
| 91 | +pass |
| 92 | + |
| 93 | + |
| 94 | +defodd(self,printNumber:'Callable[[int], None]')->None: |
| 95 | +pass |