博客园的话插链接链接都是凉的= =

题解

我理解成能不能看到这个圆，除了最后几个圆特殊以外都是等价的，然而我凉了，因为我把圆当成线段来处理，但是，有可能一个圆完全被遮住了，还有一个缝隙，就WA了
计算几何题这点最不好，WA了会想的第一件事就是垃圾OJ卡我精度，反复WA上几次才会知道，自己算法错了

那么首先每个圆的位置取决于能被左边的圆最远推到哪里，这个就是以两圆圆心距和竖直两条半径（是个梯形）算出来就行，能被推说明圆心距必然是半径之和，不断取max并同时记录是哪个圆推的它

最后取最后一个碰到某个圆的圆，并删除他们之间所有点，特判一下第一个碰到最远距离的圆pos[i] + r[i]的最大值所在的i并删除之后的圆

为什么我叙述那么混乱可能我太久没上语文课吧（手动再见）

代码

#include <iostream>
#include <cstdio>
#include <vector>
#include <set>
#include <cstring>
#include <ctime>
#include <map>
#include <algorithm>
#include <cmath>
#define MAXN 1005
#define eps 1e-8
//#define ivorysi
#define pii pair<int,int>
#define mp make_pair
#define fi first
#define se second
using namespace std;
typedef long long int64;
typedef double db;
int N,tot,ans[MAXN],touch[MAXN];
db R[MAXN],pos[MAXN];
bool dcmp(db a,db b) {return fabs(a - b) < eps;
}
struct Point {db x,y;Point(){}Point(db _x,db _y) {x = _x;y = _y;}friend Point operator + (const Point &a,const Point &b) {return Point(a.x + b.x,a.y + b.y);}friend Point operator - (const Point &a,const Point &b) {return Point(a.x - b.x,a.y - b.y);}friend Point operator * (const Point &a,db d) {return Point(a.x * d,a.y * d);}friend Point operator / (const Point &a,db d) {return Point(a.x / d,a.y / d);}friend db operator * (const Point &a,const Point &b) {return a.x * b.y - a.y * b.x;}friend db dot(const Point &a,const Point &b) {return a.x * b.x + a.y * b.y;}db norm() {return sqrt(x * x + y * y);}
}P[MAXN];
struct Seg {Point a,b;db d;Seg(){}Seg(Point _a,Point _b) {a = _a;b = _b;d = atan2(b.y - a.y,b.x - a.x);}friend Point Cross_Point(const Seg &s,const Seg &t) {db S1 = (s.a - t.a) * (t.b - t.a);db S2 = (s.b - t.b) * (t.a - t.b);return s.a +  (s.b - s.a) * (S1 / (S1 + S2));}friend bool operator < (const Seg &s,const Seg &t) {return s.d < t.d;}
}S[MAXN];
inline db o(db x) {return x * x;}
void Solve() {//scanf("%d",&N);tot = 0;for(int i = 1 ; i <= N ; ++i) scanf("%lf",&R[i]);db L = 0.0;for(int i = 1 ; i <= N ; ++i) {pos[i] = R[i];touch[i] = 0;for(int j = 1 ; j < i ; ++j) {db x = pos[j] + sqrt(R[i] * R[j]) * 2;if(x > pos[i] + eps) {pos[i] = x;touch[i] = j;}}L = max(L,pos[i] + R[i]);}int last = 0;while(1) {if(dcmp(pos[last] + R[last],L)) {for(int i = last + 1 ; i <= N ; ++i) ans[++tot] = i;break;}int v = 0;for(int i = last + 1 ; i <= N ; ++i) {if(touch[i] == last) v = i;} for(int i = last + 1 ; i < v ; ++i) ans[++tot] = i;last = v;}   printf("%d\n",tot);for(int i = 1 ; i <= tot ; ++i) {printf("%d\n",ans[i]);}
}
int main() {
#ifdef ivorysifreopen("f1.in","r",stdin);
#endifwhile(scanf("%d",&N) != EOF && N) {Solve();}return 0;
}