求连续子数组元素和绝对值的最大值

dp

double a[maxn];
int n;
double calc(double k) {
	double res1 = 0; //正最大
	double res2 = 0; //负最大
	double sum1 = 0, sum2 = 0;//当前正负最大
	for (int i = 1; i <= n; i++) {
		sum1 = max(sum1 + a[i]+k, a[i]+k);
		res1 = max(sum1, res1);
		sum2 = min(sum2 + a[i]+k, a[i]+k);
		res2 = min(sum2, res2);
	}
	return max(fabs(res1), fabs(res2));
}