归并虽然知道了过程但是敲起代码来还是出现各种小错误。。。唉，，，

#include 
      
        #include 
       
         #define maxn 500007 using namespace std; int a[maxn]; int n; int tmp[maxn]; __int64 ct; void merge(int s,int m,int e) {
    int i = s,j = m + 1; int k = 0; while (i <= m && j <= e)     {
    //s - m 和 m+1 —— e两个数组是已经排好序的 //如果a[i] > a[j]则说明i - m的值都大于a[j]出现逆序数         if (a[i] > a[j])         {
                ct += m - i + 1;             tmp[k++] = a[j++];         } else         {
                tmp[k++] = a[i++];         }     } while (i <= m)     tmp[k++] = a[i++]; while (j <= e)     tmp[k++] = a[j++]; for (i = 0; i < k; ++i)     {
            a[s + i] = tmp[i];     } } void mergesort(int s,int e) {
    if (s < e)     {
    int m = (s + e)/2;         mergesort(s,m);         mergesort(m + 1,e);         merge(s,m,e);     } } int main() {
    int i; while (~scanf("%d",&n))     {
    if (!n) break;         ct = 0; for (i = 0; i < n; ++i)         scanf("%d",&a[i]);         mergesort(0,n - 1);         printf("%I64d\n",ct);     } return 0; }