逆序数--二分法

逆序数：

在一个排列中，如果一对数的前后位置与大小顺序相反，即前面的数大于后面的数，那么它们就称为一个逆序。一个排列中逆序的总数就称为这个排列的逆序数。

 

#include "stdafx.h"#include <cassert>#include <iostream>using namespace std;class ReversedOrder{public:ReversedOrder(int *data, int length):elemArray(data),arrayLength(length),reverseCount(0){}~ReversedOrder(){if (elemArray){delete []elemArray;elemArray = NULL;}}void orderAll(){order(0, arrayLength - 1);}int getReversedCount(){return reverseCount;}private:void order(int left, int right){if (left >= right)return ;int mid = (left + right) / 2;order(left, mid);order(mid + 1, right);merge(left, mid, mid + 1, right);}void merge(const int start1, const int end1, const int start2, const int end2){int *tempArray = new int[end2 - start1 + 1];assert(tempArray);int tempArrayLength = end2 - start1 + 1;int tempArrayIndex = 0;int tempStart1 = start1;int tempStart2 = start2;while ((tempStart1 <= end1) && (tempStart2 <= end2)){if (elemArray[tempStart1] < elemArray[tempStart2]){tempArray[tempArrayIndex++] = elemArray[tempStart1++];}else {reverseCount += (end1 - tempStart1 + 1);tempArray[tempArrayIndex++] = elemArray[tempStart2++];}}while (tempStart1 <= end1){tempArray[tempArrayIndex++] = elemArray[tempStart1++];}while (tempStart2 <= end2){tempArray[tempArrayIndex++] = elemArray[tempStart2++];}for (tempArrayIndex = 0, tempStart1 = start1; tempArrayIndex < tempArrayLength; tempStart1++,tempArrayIndex++){elemArray[tempStart1] = tempArray[tempArrayIndex];}delete []tempArray;}int reverseCount;int *elemArray;int arrayLength;};int _tmain(int argc, _TCHAR* argv[]){int *data = NULL;int length = 0;cin >> length;data = new int[length];for(int i = 0; i < length; i++){cin >> data[i];}ReversedOrder reverse(data, length);reverse.orderAll();cout << reverse.getReversedCount() << endl;return 0;}

 

在merge函数中，进行了多次的数组的拷贝，会影响效率。