LeetCode 1116. Print Zero Even Odd

原题链接在这里：https://leetcode.com/problems/print-zero-even-odd/

题目：

You have a function printNumber that can be called with an integer parameter and prints it to the console.

For example, calling printNumber(7) prints 7 to the console.

You are given an instance of the class ZeroEvenOdd that has three functions: zero, even, and odd. The same instance of ZeroEvenOdd will be passed to three different threads:

Thread A: calls zero() that should only output 0's.
Thread B: calls even() that should only output even numbers.
Thread C: calls odd() that should only output odd numbers.

Modify the given class to output the series "010203040506..." where the length of the series must be 2n.

Implement the ZeroEvenOdd class:

ZeroEvenOdd(int n) Initializes the object with the number n that represents the numbers that should be printed.
void zero(printNumber) Calls printNumber to output one zero.
void even(printNumber) Calls printNumber to output one even number.
void odd(printNumber) Calls printNumber to output one odd number.

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"

Constraints:

1 <= n <= 1000

题解：

Use Semaphore. Semaphore(0) means each acquire needs to wait for release.

Semaphore(1) means first acquire could get it, but following acquire needs to wait for release.

Time Complexity: O(1).

Space: O(1).

AC Java:

 1 class ZeroEvenOdd {
 2     private int n;
 3     private Semaphore zeroSem;
 4     private Semaphore evenSem;
 5     private Semaphore oddSem;
 6     
 7     public ZeroEvenOdd(int n) {
 8         this.n = n;
 9         zeroSem = new Semaphore(1);
10         evenSem = new Semaphore(0);
11         oddSem = new Semaphore(0);
12     }
13 
14     // printNumber.accept(x) outputs "x", where x is an integer.
15     public void zero(IntConsumer printNumber) throws InterruptedException {
16         for(int i = 1; i <= n; i++){
17             zeroSem.acquire();
18             printNumber.accept(0);
19             if(i % 2 == 0){
20                 evenSem.release();
21             }else{
22                 oddSem.release();
23             }
24         }
25     }
26 
27     public void even(IntConsumer printNumber) throws InterruptedException {
28         for(int i = 2; i <= n; i += 2){
29             evenSem.acquire();
30             printNumber.accept(i);
31             zeroSem.release();
32         }
33     }
34 
35     public void odd(IntConsumer printNumber) throws InterruptedException {
36         for(int i = 1; i <= n; i += 2){
37             oddSem.acquire();
38             printNumber.accept(i);
39             zeroSem.release();
40         }
41     }
42 }