算法导论-Inversion Pair算法

import java.util.*;public class InversionPair {public static int inversion(int[] a, int low, int mid, int high) {int count = 0;int left_size = mid-low+2;int[] left = new int[left_size];for(int i=0; i<left_size-1; i++) {left[i]=a[low+i];}left[left_size-1]=Integer.MAX_VALUE;int right_size = high-mid+1;int[] right = new int[right_size];for(int i=0; i<right_size-1; i++) {right[i]=a[mid+1+i];}right[right_size-1]=Integer.MAX_VALUE;int size = high-low+1;int p=0, q=0;left_size--;right_size--;for(int i=0; i<size; i++) {if(left[p]>right[q]) {if(left[p]!=Integer.MAX_VALUE) {count += left_size-p;}a[i+low]=right[q++];} else {a[i+low]=left[p++];}}return count;}public static int inversionCount(int[] a, int low, int high) {if(low==high) {return 0;}int mid = low + (high-low)/2;int count = inversionCount(a, low, mid);count += inversionCount(a, mid+1, high);count += inversion(a, low, mid, high);return count;}public static void main(String[] args) {int[] a = {2,3,8,6,1,0};System.out.println("Origin: " + Arrays.toString(a));int count = inversionCount(a, 0, a.length-1);System.out.println("Sorted: " + Arrays.toString(a));System.out.println("Inversion Count=" + count);}}