C++求逆序对的方法

#include <iostream>#include <vector>using namespace std;int array[] = {3, 9, 7, 4, 5, 2};const int size = sizeof array / sizeof *array;int temp[size];//int numbers[size];int reversePair(int *numbers, int start, int last, int &index, int &count){ if(start == last) return 0; int mid = (last - start) / 2 + start; reversePair(numbers, start, mid, index, count); reversePair(numbers, mid + 1, last, index, count); for(int i = start; i <= last; i++) temp[i] = numbers[i]; int index1 = start, index2 = mid + 1; index = start; while(index1 <= mid && index2 <= last) { if(temp[index1] > temp[index2]) {  numbers[index] = temp[index2];  count += mid - index1 + 1;  index++;  index2++; } else if(temp[index1] == temp[index2]) {  numbers[index] = temp[index1];  index++;  index1++;  index2++; } else if(temp[index1] < temp[index2]) {  numbers[index] = temp[index1];  index++;  index1++; } } if(index1 <= mid) { while(index1 <= mid) {  numbers[index] = temp[index1];  index++;  index1++; } } else { while(index2 <= last) {  numbers[index] = temp[index2];  index++;  index2++; } } return count;}void main(){ int count = 0; int index = 0; reversePair(array, 0, size - 1, index, count); cout << "count = " << count << endl;}