32.数组中的逆序对

class Solution {
public:
    int InversePairs(vector<int> data) {
        if ( data.size() <= 0 ) return 0 ;
        
        int length = data.size() ;
        int retVal ;
        for ( int i = 0; i < length; i++ ) {
            int n = data[i] ;
            for (int j = i + 1; j < length; j++ ) {
                if ( data[j] < n ) {
                    retVal++ ;
                }
            }
        }
        return retVal ;
    }
};

// 30.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <vector>
using namespace::std;

class Solution {
public:
	int InversePairs(vector<int> data) {
		if (data.size() <= 0) return 0;

		vector<int> copy;
		for (int i = 0; i < data.size(); i++){
			copy.push_back(data[i]);
		}
		int retVal = InversePairsCore(data, copy, 0, data.size() - 1);
		return retVal;
	}

	int InversePairsCore(vector<int>& data, vector<int>& copy, int start, int end) {
		if (start == end) {
			copy[start] = data[start];
			return 0;
		}


		int length = (end - start) / 2;

		int left = InversePairsCore(copy, data, start, start + length);
		int right = InversePairsCore(copy, data, start + length + 1, end);

		int i = start + length;
		int j = end;
		int indexOfCopy = end;
		int count = 0;
		while (i >= start && j >= start + length + 1) {
			if (data[i] > data[j]) {
				copy[indexOfCopy--] = data[i--];
				count += j - start - length;
			}
			else {
				copy[indexOfCopy--] = data[j--];
			}
		}
		for (; i >= start; --i)
			copy[indexOfCopy--] = data[i];
		for (; j >= start + length + 1; --j)
			copy[indexOfCopy--] = data[j];

		return left + right + count;
	}
};
int _tmain(int argc, _TCHAR* argv[])
{
	vector<int> test;
	test.push_back(7);
	test.push_back(5);
	test.push_back(6);
	test.push_back(4);

	Solution s;
	int result = s.InversePairs(test);
	return 0;
}