题意：

给定n个x轴上的点

x w

选一个点 X 使得 

for(int i = 1; i <= n; i++) dis(X, xi)^3 * w;

最小

T^T看过了这么多人只能猜三分。。

凑一下数据大概能感觉出来

#include <cstring>
#include <cstdio>
#include <algorithm>
using namespace std;
typedef long long ll;
const int N = 50005;
double a[N], b[N];
int n;
double cal(double x) {
	double ans = 0;
	for(int i = 1; i <= n; i ++) {
		double tmp = a[i] - x;
		if(tmp < 0) tmp *= -1;
		ans += tmp * tmp * tmp * b[i];
	}
	return ans;
}
int main() {
	int T, cas = 0;
	scanf("%d", &T);
	while(T-- > 0) {
		double l = 1e10, r = -1e10;
		scanf("%d", &n);
		for(int i = 1; i <= n; i ++) {
			scanf("%lf%lf", &a[i], &b[i]);
			l = min(l, a[i]);
			r = max(r, a[i]);
		}
		for(int i = 0; i < 100; i ++) {
			double m1 = l + (r-l) / 3;
			double m2 = r - (r-l) / 3;
			if(cal(m1) < cal(m2)) r = m2;
			else l = m1;
		}
		printf("Case #%d: %.0f\n", ++cas, cal(l));
	}
	return 0;
}

HDU 4355 Party All the Time 三分