HDU3507 Print Article(斜率优化DP)

#include<cstdio>
#include<cstring>
using namespace std;
const int MAXN = 1e6 + 10, INF = 1e9 + 10;
int N, M, a[MAXN], s[MAXN], f[MAXN], q[MAXN];
int X(int x) {
    return s[x];
}
int Y(int x) {
    return f[x] + s[x] * s[x];
}
int check(int x, int y, int i) {
    return (Y(y) - Y(x)) <= (X(y) - X(x)) * 2 * s[i];
}
int check2(int xx1, int yy1, int xx2, int yy2) {
    return ((Y(yy1) - Y(xx1)) * (X(yy2) - X(xx2))) >= ((Y(yy2) - Y(xx2)) * (X(yy1) - X(xx1)));
}
/*int slope(int x, int y) {
    return (Y(y) - Y(x)) / (X(y) - X(x));
}*/
int main() {
    //freopen("a.in", "r", stdin);
    while(scanf("%d %d", &N, &M) != EOF) {
        memset(f, 0, sizeof(f)); 
        for(int i = 1; i <= N; i++) scanf("%d", &a[i]), s[i] = s[i - 1] + a[i];
        int h = 0, t = 0;
        for(int i = 1; i <= N; i++) {
        //    if(h < t)    printf("%lf %lf\n", slope(q[h], q[h + 1]), (double)2 * s[i]);
            while(h < t && check(q[h], q[h + 1], i)) h++;
            f[i] = (f[q[h]] + (s[i] - s[q[h]]) * (s[i] - s[q[h]]) + M);
            while(h < t && check2(q[t - 1], q[t], q[t], i)) t--;
            q[++t] = i;
        }
        printf("%d\n", f[N]);
    }
    return 0;
}