思路：

斜率优化dp

s[i]表示1-i的前缀和

斜率不等式为:

对于 i < j < k

（dp[j] - dp[k] + (j + s[j])^2 - (k + s[k])^2) / ((j + s[j]) - (k + s[k]))  <= 2*(i + s[i] - l -1)

#include
     
      using namespace std;#define fi first#define se second#define pi acos(-1.0)#define LL long long//#define mp make_pair#define pb push_back#define ls rt<<1, l, m#define rs rt<<1|1, m+1, r#define ULL unsigned LL#define pll pair
      
       #define pii pair
       
        #define piii pair
        
         #define mem(a, b) memset(a, b, sizeof(a))#define fio ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);#define fopen freopen("in.txt", "r", stdin);freopen("out.txt", "w", stout);//headconst int N = 5e4 + 5;int c[N], l;LL sum[N], dp[N];LL get_down(int j, int k) {    return (j + sum[j] - (k + sum[k]));}LL get_up(int j, int k) {    return dp[j] - dp[k] + (j + sum[j])*(j + sum[j]) - (k + sum[k])*(k + sum[k]);}int main() {    int n;    scanf("%d %d", &n, &l);    for (int i = 1; i <= n; i++) scanf("%d", &c[i]);    for (int i = 1; i <= n; i++) {        sum[i] = sum[i-1] + c[i];    }    deque
         
          q;    q.push_front(0);    for (int i = 1; i <= n; i++) {        while(q.size() >= 2) {            int t = q.front();            q.pop_front();            int tt = q.front();            if(get_up(tt, t) <= 2*(i + sum[i] - l - 1)*get_down(tt, t));            else {                q.push_front(t);                break;            }        }        int t = q.front();        dp[i] = dp[t] + (i - t - 1 + sum[i] - sum[t] - l) * (i - t - 1 + sum[i] - sum[t] - l);        while(q.size() >= 2) {            int t = q.back();            q.pop_back();            int tt = q.back();            if(get_up(i, t) * get_down(t, tt) <= get_up(t, tt) * get_down(i, t)) ;            else {                q.push_back(t);                break;            }        }        q.push_back(i);    }    printf("%lld\n", dp[n]);    return 0;}