先放一下我的代码，看不看随意，建议直接划到最下面。

#include <cstdio>
#include <cstring>
#include <algorithm>
#define int long long
using namespace std;

int read()
{
	int a = 0,x = 1;char ch = getchar();
	while(ch > '9' || ch < '0') {if(ch == '-') x = -1;ch = getchar();}
	while(ch >= '0' && ch <= '9') {a = a*10 + ch-'0';ch = getchar();}
	return a*x;
}

const int N=1e6+7,inf = 1e18+7;

int n,m,a[N],s[N],f[N],g[N],stk[N];

double slope(int p,int q)
{
	// printf("%d %d\n",s[p],s[q]);
	return 1.0*((s[q]-1)*(s[q]-1) + f[q] - (s[p]-1)*(s[p]-1) - f[p])/(s[q]-s[p]);
}

void calc(int val)
{
	for(int i = 1;i <= n;i ++) f[i] = -inf,g[i] = 0;
	int l=1,r=1;stk[1] = 0;
	for(int i = 1;i <= n;i ++) {
		while(l<r && slope(stk[l],stk[l+1]) < 2*s[i]) ++l;
		f[i] = f[stk[l]] + (s[i]-s[stk[l]]+1)*(s[i]-s[stk[l]]+1) + val;g[i] = g[stk[l]] + 1;
		while(l<r && slope(stk[r],i) < slope(stk[r-1],stk[r])) --r;
		stk[++r] = i;
	}
}

signed main()
{
	// freopen("random.in","r",stdin);
	// freopen("sol.out","w",stdout);
	n = read(),m = read();
	for(int i = 1;i <= n;i ++) a[i] = read();
	for(int i = 1;i <= n;i ++) s[i] = s[i-1] + a[i];
	int l = 0,r = inf,mid,ans=0;
	while(l<=r) {
		mid = l+r>>1;calc(mid);
		if(g[n] <= m) ans = mid,r = mid-1;
		else l = mid+1;
	}
	calc(ans);
//	for(int i = 1;i <= n;i ++) printf("f[%lld] = %lld ,g[%lld] = %lld\n",i,f[i],i,g[i]);
	printf("%lld",f[n] - m*ans);
	return 0;
}

我这份代码中输出的是 f[n]-ans*m ，但是我想的是 f[n] 里面应该是有 g[n] 个多余的 m，所以一开始写的是 f[n]-g[n]*ans ，但是惨遭 90pts，wa10 。那么这两者区别确实挺显然 （不是），到底哪一种是正确的呢？