九度oj 1348 数组中的逆序对

原题链接：http://ac.jobdu.com/problem.php?pid=1348 
归并排序求逆序对。。。

 #include<algorithm>
 #include<iostream>
 #include<cstdlib>
 #include<cstring>
 #include<cstdio>
 typedef unsigned long long ull;
 const int Max_N = ;
 ull res;
 int arr[Max_N], temp[Max_N];
 void Merge(int *A, int l, int m, int r) {
     int p = ;
     int x = l, y = m + ;
     while (x <= m && y <= r) {
         if (A[x] > A[y]) res += m - x + , temp[p++] = A[y++];
         else temp[p++] = A[x++];
     }
     while (x <= m) temp[p++] = A[x++];
     while (y <= r) temp[p++] = A[y++];
     for (x = ; x < p; x++) A[l + x] = temp[x];
 }
 void MergeSort(int *A, int l, int r) {
     int mid;
     if (l < r) {
         mid = (l + r) >> ;
         MergeSort(A, l, mid);
         MergeSort(A, mid + , r);
         Merge(A, l, mid, r);
     }
 }
 int main() {
 #ifdef LOCAL
     freopen("in.txt", "r", stdin);
     freopen("out.txt", "w+", stdout);
 #endif
     int n;
     while (~scanf("%d", &n)) {
         res = ;
         for (int i = ; i < n; i++) scanf("%d", &arr[i]);
         MergeSort(arr, , n - );
         printf("%lld\n", res);
     }
     return ;
 }