AtCoder - 2581 Meaningful Mean
Problem Statement
You are given an integer sequence of length N, a= {a1,a2,…,aN}, and an integer K.
a has N(N+1)⁄2 non-empty contiguous subsequences, {al,al+1,…,ar} (1≤l≤r≤N). Among them, how many have an arithmetic mean that is greater than or equal to K?
Constraints
- All input values are integers.
- 1≤N≤2×105
- 1≤K≤109
- 1≤ai≤109
Input
Input is given from Standard Input in the following format:
N K a1 a2 : aN
Output
Print the number of the non-empty contiguous subsequences with an arithmetic mean that is greater than or equal to K.
Sample Input 1
3 6
7
5
7
Sample Output 1
5
All the non-empty contiguous subsequences of a are listed below:
- {a1} = {7}
- {a1,a2} = {7,5}
- {a1,a2,a3} = {7,5,7}
- {a2} = {5}
- {a2,a3} = {5,7}
- {a3} = {7}
Their means are 7, 6, 19⁄3, 5, 6 and 7, respectively, and five among them are 6or greater. Note that {a1} and {a3} are indistinguishable by the values of their elements, but we count them individually.
Sample Input 2
1 2
1
Sample Output 2
0
Sample Input 3
7 26
10
20
30
40
30
20
10
Sample Output 3
13
树状数组sb题。
#include<bits/stdc++.h> #define ll long long using namespace std; const int maxn=200005; ll num[maxn],a[maxn],ans; int n,r[maxn],f[maxn],k,ky; inline int read(){ int x=0; char ch=getchar(); for(;!isdigit(ch);ch=getchar()); for(;isdigit(ch);ch=getchar()) x=x*10+ch-'0'; return x; } inline void update(int x,int y){ for(;x<=ky;x+=x&-x) f[x]+=y;} inline int query(int x){ int an=0; for(;x;x-=x&-x) an+=f[x]; return an;} int main(){ scanf("%d%d",&n,&k); for(int i=1;i<=n;i++) a[i]=read()-k; for(int i=1;i<=n;i++){ a[i]+=a[i-1],num[i]=a[i]; if(a[i]>=0) ans++; } sort(num+1,num+n+1); ky=unique(num+1,num+n+1)-num-1; for(int i=1;i<=n;i++) r[i]=lower_bound(num+1,num+ky+1,a[i])-num; for(int i=1;i<=n;i++) ans+=(ll)query(r[i]),update(r[i],1); printf("%lld\n",ans); return 0; }