E - Amusement Park

题目描述：

思路：

#include <bits/stdc++.h>
using namespace std;

#define endl '
'
#define inf 0x3f3f3f3f
#define mod 1000000007
#define m_p(a,b) make_pair(a, b)
#define mem(a,b) memset((a),(b),sizeof(a))
#define io ios::sync_with_stdio(false); cin.tie(0); cout.tie(0)

typedef long long ll;
typedef pair <int,int> pii;

#define MAX 300000 + 50
ll n, m, k;
ll tr[MAX];

bool check(ll mid){
    m = 0;
    for(int i = 1; i <= n; ++i){
        m += max(0ll, tr[i] - mid);
    }
    if(m < k)return true;
    else return false;
}

void work(){
    cin >> n >> k;
    for(int i = 1; i <= n; ++i){
        cin >> tr[i];
    }
    ll l = 0, r = 2000000001;
    while (l <= r) {
        ll mid = (l + r) / 2;
        if(check(mid))r = mid - 1;
        else l = mid + 1;
    }
    ll ans = 0;
    ++l;
    for(int i = 1; i <= n; ++i){
        if(tr[i] < l)continue;
        k -= (tr[i] - l + 1);
        ans += max(0ll, (tr[i] - l + 1) * (tr[i] + l) / 2);
    }
    --l;
    while (k--) {
        ans += l;
    }
    cout << ans << endl;
    
}


int main(){
    io;
    work();
    return 0;
}