HDOJ2838(树状数组)

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#define MAXN 100001
using namespace std;
struct tree
{
int t;
long long sum;
}tree[MAXN];
int n;
int lowbit(int i)
{
return i&(-i);
}
void update(int i, int s, int x)
{
while (i <= n)
{
tree[i].t += x;
tree[i].sum += s;
i = i + lowbit(i);
}
}
int queryx(int n)
{
int ans = 0;
while (n > 0)
{
ans += tree
.t;
n -= lowbit(n);
}
return ans;
}
long long  querysum(int n)
{
long long ans = 0;
while (n > 0)
{
ans += tree
.sum;
n -= lowbit(n);
}
return ans;
}
int main()
{
while (~scanf("%d", &n))
{
long long ans = 0;
memset(tree, 0, sizeof(tree));
for (int i = 1; i <= n; i++)
{
int a;
scanf("%d", &a);
update(a, a, 1);
long long k = i - queryx(a);
if (k != 0)
{
long long k1 = querysum(n) - querysum(a);//前n个数之和减去比a小的数之和，即比a大的数之和。
ans += k*a + k1;
}
}
printf("%lld\n", ans);
}
return 0;
}