B 二分

题意

样例

5 3 10
3 4 2 1 5

12

 找最右边的L下标即可

思路

二分最靠右的L端点，R端点取最右端(n*k处)，找到后，答案就是L的位置(pos)，（因为如果pos满足，则pos左边的所有下标都满足

代码 

const int N = 2e5 + 10;


LL n,m,k;
LL x;
LL a[N],suf[N];

bool check(LL mid)
{
	LL t = (n * k - mid + 1) / n * suf[1];
	t += suf[n + 1 - (n * k - mid + 1) % n];
	return t >= x;
}

void solve() 
{	
	memset(a,0,sizeof a);
	memset(suf,0,sizeof suf);
	
	cin >> n >> k >> x;
	for (int i = 1;i <= n;i ++)	 cin >> a[i];
	
	for (int i = n;i >= 1;i --) suf[i] = suf[i + 1] + a[i];
	
	if (suf[1] * k < x) 
	{
		cout << 0 << endl;
		return;
	}
	if (a[n] >= x)
	{
		cout << n * k << endl;
		return;
	}
	 
	LL l = 0,r = n * k + 1;
	while(l + 1 != r)
	{
		LL mid = l + r >> 1;
		if (check(mid)) l = mid;
		else r = mid;
	}
	if (check(l)) cout << l << endl;
	else cout << r << endl;
	
}