Inversions (Algorithms 4/e)

Object
- edu.princeton.cs.algs4.Inversions

```
public class Inversions
extends Object
```
The Inversions class provides static methods to count the number of inversions in either an array of integers or comparables. An inversion in an array a[] is a pair of indicies i and j such that i < j and a[i] > a[j].
This implementation uses a generalization of mergesort. The count operation takes Θ(n log n) time to count the number of inversions in any array of length n (assuming comparisons take constant time).
For additional documentation, see Section 2.2 of Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne.

Author:

Robert Sedgewick, Kevin Wayne

Method Summary

All Methods Static Methods Concrete Methods
Modifier and Type	Method	Description
`static long`	`count(int[] a)`	Returns the number of inversions in the integer array.
`static <Key extends Comparable<Key>> long`	`count(Key[] a)`	Returns the number of inversions in the comparable array.
`static void`	`main(String[] args)`	Reads a sequence of integers from standard input and prints the number of inversions to standard output.

Methods inherited from class java.lang.Object
clone, equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Method Detail
  - count
```
public static long count(int[] a)
```
    Returns the number of inversions in the integer array. The argument array is not modified.
    
    Parameters:
    
    a - the array
    
    Returns:
    
    the number of inversions in the array. An inversion is a pair of indicies i and j such that i < j and a[i] > a[j].
  - count
```
public static <Key extends Comparable<Key>> long count(Key[] a)
```
    Returns the number of inversions in the comparable array. The argument array is not modified.
    
    Type Parameters:
    
    Key - the inferred type of the elements in the array
    
    Parameters:
    
    a - the array
    
    Returns:
    
    the number of inversions in the array. An inversion is a pair of indicies i and j such that i < j and a[i].compareTo(a[j]) > 0.
  - main
```
public static void main(String[] args)
```
    Reads a sequence of integers from standard input and prints the number of inversions to standard output.
    
    Parameters:
    
    args - the command-line arguments