HDU5806：NanoApe Loves Sequence Ⅱ(尺取法）

题目链接：HDU5806

题意：找出有多少个区间中第k大数不小于m.

分析：用尺取法可以搞定，CF以前有一道类似的题目.

#include<cstdio>
using namespace std;
typedef long long ll;
#define d\n I64d\n
int T,n,m,K,num,r,a[200010];
ll ans;
int main()
{
    scanf("%d",&T);
    while (T--)
    {
        scanf("%d%d%d",&n,&m,&K);
        for (int i=1;i<=n;i++) scanf("%d",&a[i]);
        num=0;r=0;ans=0;
        for (int i=1;i<=n;i++)
        {
            while (num<K&&r<n){r++;num+=(a[r]>=m);}
            if (num<K) break;
            ans+=n-r+1;
            num-=(a[i]>=m);
        }
        printf("%d",ans);
    }
}