C2. Bessie's Birthday Cake (Hard Version)

原题链接

题解

假如 $y=1$ 该如何添加？

然后逐步推导

code

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

int a[200005];

bool cmp(int x,int y)
{
    if(x%2!=y%2) return x%2<y%2;
    else return x<y;
}

void solve()
{
    int n,x,y;
    cin>>n>>x>>y;

    for(int i=1;i<=x;i++) cin>>a[i];

    sort(a+1,a+1+x);
    vector<int> d;
    for(int i=1;i<=x;i++) d.push_back((a[i]+n-a[(i-2+x)%x+1])%n);

    sort(d.begin(),d.end(),cmp);


    int ans=max(0,x-2);

    for(auto it:d)
    {
        //printf("%d  ans:%d\n",it,ans);
        if(it==1) continue;
        if(it==2)
        {
            ans++;
            continue;
        }
        int cnt=(it-1)/2,judge=it%2;

        if(y>=cnt)
        {
            ans+=cnt;
            ans+=cnt;
            y-=cnt;
            if(!judge) ans++;
        }
        else
        {
            ans+=y;
            ans+=y;
            y=0;
        }
    }

    cout<<ans<<'\n';
}
int main()
{
    ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
    int t=1;
    cin>>t;
    while(t--) solve();
    return 0;
}