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POJ-2420 A Star not a Tree?
题意: 给定n个点, 找到一个点p. 使得p到所有点的距离之和最小.
分析: 模拟退火随机产生圆心坐标, 跑一遍模拟退火就行, 这题n的范围是100, 莫名其妙re, 开1000就ac了.
代码:
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <ctime>
#include <iostream>
using namespace std;
const int MAXN = 1111;
const double eps = 1e-8;
const double pi = acos(-1);
const double inf = 0x3f3f3f3f;
struct Point {
double x, y;
Point() {}
Point(double _x, double _y) {
x = _x;
y = _y;
}
double distance(Point b) { return hypot(x - b.x, y - b.y); }
};
Point p[MAXN];
int n;
Point ans;
double Rand() { return (double)rand() / RAND_MAX; }
double getdis(Point b) {
double res = 0;
for (int i = 0; i < n; i++) {
res += b.distance(p[i]);
}
return res;
}
int main() {
srand(0);
while (scanf("%d", &n) != EOF) {
ans.x = 0, ans.y = 0;
for (int i = 0; i < n; i++) {
scanf("%lf%lf", &p[i].x, &p[i].y);
ans.x += p[i].x;
ans.y += p[i].y;
}
ans.x /= n;
ans.y /= n;
double t = 100000;
double res = getdis(ans);
Point nxt;
while (t > eps) {
nxt.x = ans.x + t * (Rand() * 2 - 1);
nxt.y = ans.y + t * (Rand() * 2 - 1);
double dis = getdis(nxt);
if (res > dis) {
res = dis;
ans = nxt;
}
t *= 0.97;
}
printf("%.0f", res);
}
return 0;
}