CF1005E2 Median on Segments (General Case Edition)（树状数组）

题意：

给出一个序列，询问中位数为m的子序列数量（这里的子序列要求连续）

题解：

 

#include<bits/stdc++.h>
using namespace std;
const int maxn=1e6+100;
typedef long long ll;
#define lowbit(x) x&-x
int a[maxn];
int b[maxn];
int c[maxn];
int n,m;
void add (int x,int val) {
    for (int i=x;i<maxn;i+=lowbit(i)) c[i]+=val;
}
int getsum (int x) {
    int ans=0;
    for (int i=x;i;i-=lowbit(i)) ans+=c[i];
    return ans;
}
ll wjm (int n,int m) {
    for (int i=1;i<=n;i++) a[i]<=m?(b[i]=1):(b[i]=-1);
    for (int i=1;i<=n;i++) b[i]+=b[i-1];
    memset(c,0,sizeof(c));
    add(n+1,1);
    ll ans=0;
    for (int i=1;i<=n;i++) ans+=getsum(n+1+b[i]),add(b[i]+n+1,1);
    return ans;
}
int main () {
    cin>>n>>m;
    for (int i=1;i<=n;i++) cin>>a[i];
    cout<<wjm(n,m)-wjm(n,m-1)<<endl;
}