【HDOJ】2440 Watch out the Animal

刚开始学随机算法，凸包+模拟退火。

/* 2440 */
#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <algorithm>
using namespace std;

#define MAXN 105

typedef struct {
    int x, y;
} Point_t;

Point_t stack[MAXN];
Point_t points[MAXN];
int dir[8][2] = {
    {-1, 0}, {1, 0}, {0, -1}, {0, 1},
    {-1, -1}, {-1, 1}, {1, -1}, {1, 1}
};
const double eps = 1e-10;
const double next = 0.9;
int n, top;
int ans;

double Length(Point_t a, Point_t b) {
    return sqrt( (a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y) + 0.);
}

int Length2(Point_t a, Point_t b) {
    return (a.x-b.x)*(a.x-b.x) + (a.y-b.y)*(a.y-b.y);
}

int cross(Point_t a, Point_t b, Point_t c) {
    return (b.x-a.x)*(c.y-a.y) - (c.x-a.x)*(b.y-a.y);
}

bool comp(Point_t a, Point_t b) {
    int m = cross(points[0], a, b);
    return m>0 || (m==0 && Length2(points[0], a)<Length2(points[0], b));
}

void Graham() {
    int i, j, k;
    Point_t p;
    
    p = points[0];
    k = 0;
    for (i=1; i<n; ++i) {
        if (points[i].x<p.x || (points[i].x==p.x && points[i].y<p.y)) {
            k = i;
            p = points[i];
        }
    }
    points[k] = points[0];
    points[0] = p;
    
    sort(points+1, points+n, comp);
    stack[0] = points[0];
    stack[1] = points[1];
    top = 1;
    
    for (i=2; i<n; ++i) {
        while (top>1 && cross(stack[top-1], stack[top], points[i])<=0)
            --top;
        stack[++top] = points[i];
    }
}

double cal(double xx, double yy) {
    double ret = 0;
    double x, y;
    
    for (int i=0; i<=top; ++i) {
        x = xx - stack[i].x;
        y = yy - stack[i].y;
        ret += sqrt(x*x + y*y);
    }
    
    return ret;
}

void SA() {
    double step = 10000.;
    double dis, tmp;
    double x, y;
    double xx, yy;
    int i;

    x = stack[0].x;
    y = stack[0].y;
    dis = cal(x, y);
    while (step > eps) {
        for (i=0; i<8; ++i) {
            xx = x + step * dir[i][0];
            yy = y + step * dir[i][1];
            tmp = cal(xx, yy);    
            if (tmp < dis) {
                dis = tmp;
                x = xx;
                y = yy;
            }
        }
        step *= next;
    }
    
    ans = (dis+0.5);
}

int main() {
    int t;
    int i, j, k;
    
    #ifndef ONLINE_JUDGE
        freopen("data.in", "r", stdin);
        //freopen("data.out", "w", stdout);
    #endif
    
    scanf("%d", &t);
    while (t--) {
        scanf("%d", &n);
        for (i=0; i<n; ++i)
            scanf("%d %d", &points[i].x, &points[i].y);
        Graham();
        SA();
        printf("%d
", ans);
        if (t)
            printf("
");
    }
    
    return 0;
}