poj 2420 模拟退火

题意：

给n个点，求与这n个点，距离和最接近的那个点是什么，输出这个最短距离。

解析：

模拟退火。

在acdream那里学模拟退火，准备做去年西安网赛的题目。

来自：

http://blog.youkuaiyun.com/acdreamers/article/details/10019849

代码：

#pragma comment(linker, "/STACK:1677721600")
#include <map>
#include <set>
#include <cmath>
#include <queue>
#include <stack>
#include <vector>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <climits>
#include <cassert>
#include <iostream>
#include <algorithm>
#define pb push_back
#define mp make_pair
#define LL long long
#define lson lo,mi,rt<<1
#define rson mi+1,hi,rt<<1|1
#define Min(a,b) ((a)<(b)?(a):(b))
#define Max(a,b) ((a)>(b)?(a):(b))
#define mem(a,b) memset(a,b,sizeof(a))
#define FIN freopen("in.txt", "r", stdin)
#define FOUT freopen("out.txt", "w", stdout)
#define rep(i,a,b) for(int i=(a); i<=(b); i++)
#define dec(i,a,b) for(int i=(a); i>=(b); i--)

using namespace std;
const int mod = 1e9 + 7;
const double ee = exp(1.0);
const int inf = 0x3f3f3f3f;
const int maxn = 1000 + 10;
const double pi = acos(-1.0);
const LL iinf = 0x3f3f3f3f3f3f3f3f;

int readT()
{
    char c;
    int ret = 0,flg = 0;
    while(c = getchar(), (c < '0' || c > '9') && c != '-');
    if(c == '-') flg = 1; else ret = c ^ 48;
    while( c = getchar(), c >= '0' && c <= '9') ret = ret * 10 + (c ^ 48);
    return flg ? - ret : ret;
}

const double eps = 1e-8;    //搜索停止条件
const double delta = 0.98;  //温度下降速度
const int initT = 1;      //初始温度

int dir[4][2] = {{1, 0}, {0, 1}, {-1, 0}, {0, -1}};

struct Point
{
    double x, y;
} p[maxn];

Point readPoint()
{
    Point res;
    scanf("%lf%lf", &res.x, &res.y);
    return res;
}

double dist(Point a, Point b)
{
    return sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));
}

double getSum(int n, Point t)
{
    double res = 0;
    rep(i, 0, n - 1)
        res += dist(p[i], t);
    return res;
}

double solve(int n)
{
    Point star = p[0];      //随机初始化一个点开始搜索
    double t = initT;       //初始化温度
    double ans = inf;       //初始化最优解

    while (eps < t)
    {
        bool flag = true;
        while (flag)
        {
            flag = false;
            rep(i, 0, 3)
            {
                Point now;
                now.x = star.x + dir[i][0] * t;
                now.y = star.y + dir[i][1] * t;
                double t = getSum(n, now);
                if (t < ans)
                {
                    ans = t;
                    star = now;
                    flag = true;
                }
            }
        }
        t *= delta;
    }
    return ans;
}

int main()
{
    #ifdef LOCAL
    FIN;
    #endif // LOCAL
    int n;
    while (~scanf("%d", &n))
    {
        rep(i, 0, n - 1)
        {
            p[i] = readPoint();
        }
        printf("%.0lf\n", solve(n));
    }
    return 0;
}