poj2299

树状数组

复制代码
View Code
#include <iostream>
#include
<cstdio>
#include
<cstdlib>
#include
<cstring>
#include
<algorithm>
using namespace std;

#define maxn 500005

struct Elem
{
int p, v;
}s[maxn];

int f[maxn];
int pos[maxn];
int ar[maxn];

bool operator < (const Elem &a, const Elem &b)
{
return a.v < b.v;
}

int lowb(int t)
{
return t & (-t);
}

void add(int i, int v)
{
for (; i < maxn; ar[i] +=v, i += lowb(i));
}

int sum(int i)
{
int s = 0;
for (; i > 0; s += ar[i], i -= lowb(i));
return s;
}

int main()
{
//freopen("t.txt", "r", stdin);
int n;
memset(ar,
0, sizeof(ar));
while (scanf("%d", &n), n)
{
memset(ar,
0, sizeof(ar));
for (int i = 0; i < n; i++)
{
scanf(
"%d", &f[i]);
s[i].v
= f[i];
s[i].p
= i;
}
sort(s, s
+ n);
for (int i = 0; i < n; i++)
pos[s[i].p]
= i + 1;
long long ans = 0;
for (int i = n - 1; i >= 0; i--)
{
ans
+= sum(pos[i] - 1);
add(pos[i],
1);
}
printf(
"%lld\n", ans);
}
return 0;
}
复制代码

posted @   undefined2024  阅读(319)  评论(0编辑  收藏  举报
努力加载评论中...
点击右上角即可分享
微信分享提示