1042.D Petya and Array 前缀 + 树状数组

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
typedef long long ll;
const int maxn = 2e5 + 1e3;
ll sum[maxn];
ll f[maxn];
ll tree[maxn];
int n;
ll lowbit(ll x)
{
    return x & (-x);
}
void add(ll x)
{
    while(x <= n+1)
    {
        ++tree[x];
        x += lowbit(x);
    }
}
ll Get(ll x)
{
    ll ans = 0;
    while(x > 0)
    {
        ans += tree[x];
        x -=lowbit(x);
    }
    return ans;
}
int main()
{
    ll t;
    while(~scanf("%d %lld",&n,&t))
    {
        memset(sum,0,sizeof(sum));
        memset(tree,0,sizeof(tree));
        for(int i = 1;i <= n;++i)
        {
            scanf("%lld",&sum[i]);
            sum[i] += sum[i-1];
            f[i] = sum[i];
        }
        f[0] = 0;
        sort(f,f+n+1);
        ll ans = 0;
        for(int i = 1;i <= n;++i)
        {
            add(lower_bound(f,f+n+1,sum[i-1]) + 1 - f);
            ans += i - Get(lower_bound(f,f+n+1,sum[i] - t + 1) - f);
        }
        printf("%lld\n",ans);
    }
    return 0;
}