【HDOJ】1348 Wall

计算几何-凸包模板题目，Graham算法解。

/* 1348 */
#include <iostream>
#include <cstdio>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <algorithm>
using namespace std;

#define MAXN 1005

typedef struct Point_t {
    double x, y;
    Point_t() {}
    Point_t(double xx, double yy) {
        x = xx; y = yy;
    }
} Point_t;

Point_t stack[MAXN];
Point_t points[MAXN];
const double PI = acos(-1.0);
int n;

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));
}

double cross(Point_t p0, Point_t p1, Point_t p2) {
    return (p1.x - p0.x) * (p2.y - p0.y) - (p2.x - p0.x) * (p1.y - p0.y);
}

bool comp(Point_t a, Point_t b) {
    double k = cross(points[0], a, b);
    return !(k<0 || (k==0 && Length(points[0], a)>Length(points[0], b)));
}

double Graham() {
    double ret = 0;
    int i, j, k;
    int top;
    Point_t p0;
    
    p0 = points[0];
    k = 0;
    for (i=1; i<n; ++i) {
        if (points[i].x<p0.x || (points[i].x==p0.x && points[i].y<p0.y)) {
            p0 = points[i];
            k = i;
        }
    }
    
    points[k] = points[0];
    points[0] = p0;
    sort(points+1, points+n, comp);
    
    stack[0] = points[0];
    stack[1] = points[1];
    stack[2] = points[2];
    top = 2;
    for (i=3; i<n; ++i) {
        while (cross(stack[top-1], stack[top], points[i])<=0 && top>1)
            --top;
        stack[++top] = points[i];
    }
    stack[++top] = p0;
    for (i=1; i<=top; ++i)
        ret += Length(stack[i-1], stack[i]);
    
    return ret;
}

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