开始数组开小了20pts，后面开大了40pts,多数节点re，求助大佬修正
by Faded_wind123 @ 2024-04-06 15:43:26
注意到n>=5*10 5
或许你需要学习归并排序或者是树状数组 推荐前者
by hair_loss_tree @ 2024-04-06 15:54:17
@[hair_loss_tree](/user/1057595) 不是<=吗
by Faded_wind123 @ 2024-04-06 16:01:11
@[hair_loss_tree](/user/1057595) 好的，我去学下
by Faded_wind123 @ 2024-04-06 16:03:17
```cpp
#include <bits/stdc++.h>
using namespace std;
const int N = 1e6 + 10;
long long a[N], tmp[N], sum=0;
void merge_sort(long long q[], long long l, long long r) {
if (l >= r) return;
int mid = l + r >> 1;
merge_sort(q, l, mid), merge_sort(q, mid + 1, r);
int k = 0, i = l, j = mid + 1;
while (i <= mid && j <= r)
if (q[i] <= q[j]) tmp[k ++ ] = q[i ++ ];
else{
tmp[k ++ ] = q[j ++ ];
sum+=mid-i+1;
}
while (i <= mid) tmp[k ++ ] = q[i ++ ];
while (j <= r) tmp[k ++ ] = q[j ++ ];
for (i = l, j = 0; i <= r; i ++, j ++ ) q[i] = tmp[j];
}
int main() {
int n;
cin>>n;
for (int i = 0; i < n; i ++ ) cin>>a[i];
merge_sort(a, 0, n - 1);
cout<<sum;
return 0;
}
```
by Laihaocheng @ 2024-04-06 16:07:40
@[Laihaocheng](/user/1069294) 感谢佬，我尽量尝试理解下 ，关注了
by Faded_wind123 @ 2024-04-06 16:29:42