HDU 1348 Wall

题目链接

就是求出凸包，计算凸包周长，然后加上圆周长即可

代码：

#include<cstdio>
#include<cmath>
#include<algorithm>
using namespace std;

const int MAXN=1000;

struct Point {
    int x, y;
} list[MAXN];

int stack[MAXN], top;

int xmult(Point p0, Point p1, Point p2) {
    return (p1.x - p0.x) * (p2.y - p0.y) - (p1.y - p0.y) * (p2.x - p0.x);
}

double dist(Point p1,Point p2) {
    return sqrt((double)(p2.x-p1.x)*(p2.x-p1.x)+(p2.y-p1.y)*(p2.y-p1.y));
}

//极角排序函数 ， 角度相同则距离小的在前面
bool cmp(Point p1,Point p2)  {
    int tmp= xmult(list[0], p1, p2);
    if(tmp > 0) return true;
    else if(tmp == 0 && dist(list[0], p1) < dist(list[0], p2)) return true;
    else return false;
}

//输入并把最左下方的点放在list[0]并且进行极角排序
void init(int n)  {
    int i, k;
    Point p0;
    scanf("%d%d", &list[0].x, &list[0].y);
    p0.x = list[0].x;
    p0.y = list[0].y;
    k = 0;
    for(i = 1; i < n; i++) {
        scanf("%d%d", &list[i].x, &list[i].y);
        if((p0.y > list[i].y) || ((p0.y == list[i].y) && (p0.x > list[i].x))) {
            p0.x = list[i].x;
            p0.y = list[i].y;
            k = i;
        }    
    }    
    list[k] = list[0];
    list[0] = p0;
    sort(list + 1, list + n, cmp);
}     

void graham(int n) {
    int i;
    if(n == 1) {top = 0; stack[0] = 0;}
    if(n == 2) {
        top = 1;
        stack[0] = 0;
        stack[1] = 1;
    }
    if(n > 2) {
        for(i = 0; i <= 1; i++) stack[i] = i;
        top = 1;
        for(i = 2; i < n; i++) {
            while(top > 0 && xmult(list[stack[top - 1]], list[stack[top]], list[i]) <= 0) top--;
            top++;
            stack[top]=i;
        }
    }
}

const double pi = acos(-1.0);
int t, n, r;

int main() {
	scanf("%d", &t);
	while (t--) {
		scanf("%d%d", &n, &r);
		init(n);
		graham(n);
		double ans = 2 * pi * r;
		for (int i = 0; i < top; i++)
			ans += dist(list[stack[i]], list[stack[i + 1]]);
		ans += dist(list[stack[top]], list[stack[0]]);
		printf("%.0lf\n", ans);
		if (t) printf("\n");
	}
	return 0;
}