写出他的解题思路和代码实验环境为DEV C++
时间: 2024-03-10 19:46:13 浏览: 19
解题思路:
1. 读入数据;
2. 使用归并排序的思想,对序列进行排序,并计算逆序对数;
3. 输出逆序对数。
代码实现:
```c++
#include <cstdio>
#include <cstdlib>
const int MAXN = 500005;
int a[MAXN], tmp[MAXN];
long long ans;
void merge_sort(int l, int r)
{
if (l >= r) return;
int mid = (l + r) >> 1;
merge_sort(l, mid);
merge_sort(mid + 1, r);
int i = l, j = mid + 1, k = l;
while (i <= mid && j <= r) {
if (a[i] <= a[j]) {
tmp[k++] = a[i++];
} else {
tmp[k++] = a[j++];
ans += mid - i + 1;
}
}
while (i <= mid) tmp[k++] = a[i++];
while (j <= r) tmp[k++] = a[j++];
for (int i = l; i <= r; ++i) a[i] = tmp[i];
}
int main()
{
int n;
scanf("%d", &n);
for (int i = 1; i <= n; ++i) {
scanf("%d", &a[i]);
}
merge_sort(1, n);
printf("%lld\n", ans);
return 0;
}
```
实验环境:DEV C++ 5.11