【BZOJ3675】[Apio2014]序列分割【斜率优化】

写了各种姿势，最后还是得照着网上题解才能AC= =

参考了凯爷blog：http://blog.csdn.net/lethelody/article/details/44781927

#include <cstdio>
#include <algorithm>

using namespace std;

typedef long long LL;

const int maxn = 100005, maxq = maxn;

int n, k, q[maxq];
LL f[maxn][2], sum[maxn];

inline int iread() {
int f = 1, x = 0; char ch = getchar();
for(; ch < '0' || ch > '9'; ch = getchar()) f = ch == '-' ? -1 : 1;
for(; ch >= '0' && ch <= '9'; ch = getchar()) x = x * 10 + ch - '0';
return f * x;
}

inline LL y(int a, int b, int t) {
return (f[a][t] - sum[a] * sum[a]) - (f[b][t] - sum[b] * sum[b]);
}

inline LL x(int a, int b) {
return sum[a] - sum[b];
}

int main() {
n = iread(); k = iread();
for(int i = 1; i <= n; i++) sum[i] = iread() + sum[i - 1];

for(int j = 1; j <= k; j++) {
int h = 1, t = 1; q[h] = j;
for(int i = j + 1; i <= n; i++) {
for(; h < t && y(q[h + 1], q[h], ~j & 1) >= -sum[i] * x(q[h + 1], q[h]); h++);
f[i][j & 1] = f[q[h]][~j & 1] + sum[q[h]] * (sum[i] - sum[q[h]]);
for(; h < t && y(q[t], q[t - 1], ~j & 1) * x(i, q[t]) <= y(i, q[t], ~j & 1) * x(q[t], q[t - 1]); t--);
q[++t] = i;
}
}

printf("%lld\n", f
[k & 1]);
return 0;
}