Package g1101_1200.s1117_building_h2o

Class H2O

java.lang.Object
g1101_1200.s1117_building_h2o.H2O
public class H2O extends java.lang.Object
1117 - Building H2O.

Medium

There are two kinds of threads: oxygen and hydrogen. Your goal is to group these threads to form water molecules.

There is a barrier where each thread has to wait until a complete molecule can be formed. Hydrogen and oxygen threads will be given releaseHydrogen and releaseOxygen methods respectively, which will allow them to pass the barrier. These threads should pass the barrier in groups of three, and they must immediately bond with each other to form a water molecule. You must guarantee that all the threads from one molecule bond before any other threads from the next molecule do.

In other words:

  • If an oxygen thread arrives at the barrier when no hydrogen threads are present, it must wait for two hydrogen threads.
  • If a hydrogen thread arrives at the barrier when no other threads are present, it must wait for an oxygen thread and another hydrogen thread.

We do not have to worry about matching the threads up explicitly; the threads do not necessarily know which other threads they are paired up with. The key is that threads pass the barriers in complete sets; thus, if we examine the sequence of threads that bind and divide them into groups of three, each group should contain one oxygen and two hydrogen threads.

Write synchronization code for oxygen and hydrogen molecules that enforces these constraints.

Example 1:

Input: water = “HOH”

Output: “HHO”

Explanation: “HOH” and “OHH” are also valid answers.

Example 2:

Input: water = “OOHHHH”

Output: “HHOHHO”

Explanation: “HOHHHO”, “OHHHHO”, “HHOHOH”, “HOHHOH”, “OHHHOH”, “HHOOHH”, “HOHOHH” and “OHHOHH” are also valid answers.

Constraints:

  • 3 * n == water.length
  • 1 <= n <= 20
  • water[i] is either 'H' or 'O'.
  • There will be exactly 2 * n 'H' in water.
  • There will be exactly n 'O' in water.

  • Nested Class Summary

    Nested Classes
    Modifier and Type
    Class
    Description
    static class 
    H2O.HydrogenRunnable
     
    static class 
    H2O.OxygenRunnable
     

  • Constructor Summary

    Constructors
    Constructor
    Description
    H2O()
     

  • Method Summary

    Modifier and Type
    Method
    Description
    void
    hydrogen(java.lang.Runnable releaseHydrogen)
     
    void
    oxygen(java.lang.Runnable releaseOxygen)
     

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Constructor Details

    • H2O

      public H2O()

  • Method Details

    • hydrogen

      public void hydrogen(java.lang.Runnable releaseHydrogen) throws java.lang.InterruptedException
      Throws:
      java.lang.InterruptedException

    • oxygen

      public void oxygen(java.lang.Runnable releaseOxygen) throws java.lang.InterruptedException
      Throws:
      java.lang.InterruptedException