【Codeforces 1042D】Petya and Array

【链接】 我是链接,点我呀:)

【题意】

题意

【题解】

把a[i]处理成前缀和
离散化.
枚举i从1..n假设a[i]是区间和的a[r]
显然我们需要找到a[r]-a[l]

【代码】

#include <bits/stdc++.h>
#define ll long long
using namespace std;
const int N = 2e5;
int n;
ll t;
ll a[N+10];
ll b[N*2+10];
map<ll,int> dic,dic1;
int lowbit(int x){
    return x&(-x);
}
ll get_sum(int x){
    ll ans = 0;
    while (x>0){
        ans = ans + b[x];
        x = x-lowbit(x);
    }
    return ans;
}
void add(int x){
    while (x<=2*N+2){
        b[x]= b[x]+1;
        x = x + lowbit(x);
    }
}
int main(){
    ios::sync_with_stdio(0),cin.tie(0);
    cin >> n >> t;
    dic[0] = 1;
    dic[0+t] = 1;
    for (int i = 1;i <= n;i++) {
        cin >> a[i];
        a[i]+=a[i-1];
        dic[a[i]] = 1;
        dic[a[i]+t] = 1;
    }
    int cnt = 0;
    for (auto temp:dic){
        cnt++;
        dic1[temp.first] = cnt;
    }
    add(dic1[0+t]);
    //cout<<dic1[0+t]<<endl;
    ll fans = 0;
    for (int i = 1;i <= n;i++){
        ll temp1 = get_sum(cnt)-get_sum(dic1[a[i]]);
        fans = fans + temp1;
        add(dic1[a[i]+t]);
    }
    cout<<fans<<endl;
    return 0;
}