APIO2010 特别行动队

#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
const int N = 1000005;
int q[2*N], a, b, c; LL f
, s
;
double cal (int x, int y) {
LL sdt = (LL)s[y]*s[y]-s[x]*s[x]; LL dt = (LL)s[y]-s[x];
LL dty = (LL)f[y]-f[x]+a*sdt-b*dt; LL dtx = (LL)2*a*dt;
return 1.0*dty/dtx;
}
int main () {
int n, x, l = 0, r = 0;
scanf ("%d%d%d%d", &n, &a, &b, &c);
for (int i = 1; i <= n; ++ i) {
scanf ("%d", &x); s[i] = s[i-1]+x;
}
for (int i = 1; i <= n; ++ i) {
while (l<r && cal (q[l], q[l+1])<s[i]) ++l;
LL dt = (LL)s[i]-s[q[l]]; LL dts = (LL)dt*dt;
f[i] = (LL)f[q[l]]+a*dts+b*dt+c;
while (l<r && cal (q[r-1], q[r])>cal (q[r], i)) --r;
q[++r] = i;
} printf ("%lld\n", f
);
return 0;
}