poj1007 归并求逆序对

简单的归并求逆序对，再结构体排序。

#include <iostream>
#include <algorithm>
using namespace std;

#define N 55
#define M 105

char tmp[N], a[N]; 
int ans;

struct Node
{
    char s[N];
	int k;
} str[M];

void Merge(int l_sta, int r_sta, int r_end, char a[])
{
	int l_end = r_sta - 1;
    int size = r_end - l_sta + 1;
	int id = l_sta, i;
       
	while(l_sta <= l_end && r_sta <= r_end)
	      if(a[l_sta] <= a[r_sta])
			  tmp[id++] = a[l_sta++];
		  else {
			  tmp[id++] = a[r_sta++];
              ans += l_end - l_sta + 1;//由于a[l_sta]~a[l_end]都是大于a[r_sta]的，所以构成l_end - l_sta + 1个逆序对
		  }
	while(l_sta <= l_end)
		tmp[id++] = a[l_sta++];
	while(r_sta <= r_end)
		tmp[id++] = a[r_sta++];
	for(i = 1; i <= size; i++, r_end--)
	    a[r_end] = tmp[r_end];
}

void MSort(int l, int r, char a[])
{
	int c;

    if(l < r)
	{
		c = ( l + r ) / 2;
        MSort(l, c, a);
		MSort(c + 1, r, a);
		Merge(l, c + 1, r, a);
	}
}

bool compare(const Node &a, const Node &b)
{
	return a.k < b.k;
}

int main()
{
	int n, m, i;

    scanf("%d%d", &n, &m);
	getchar();
	for(i = 0; i < m; i++)
	{
		scanf("%s", a);
		getchar();
		ans = 0;
		strcpy(str[i].s, a);
		MSort(0, n-1, a);
		str[i].k = ans;
	}
    sort(str, str+m, compare);
	for(i = 0; i < m; i++)
		printf("%s\n", str[i].s);
	return 0;
}