如果两点的连线不和墙相交，那么在图中为这两点连一条边，权值为这两点的距离
然后做 Dijkstra
/**//*************************************************************************
Author: WHU_GCC
Created Time: 2007-8-12 19:53:33
File Name: pku1556.cpp
Description:
************************************************************************/
#include <iostream>
#include <cmath>
#include <vector>
#include <map>
#define maxn 1010
using namespace std;
#define out(x) (cout << #x << ": " << x << endl)
typedef long long int64;
const int maxint = 0x7FFFFFFF;
const int64 maxint64 = 0x7FFFFFFFFFFFFFFFLL;
template <class T> void show(T a, int n) 
{ for (int i = 0; i < n; ++i) cout << a[i] << ' '; cout << endl; }
template <class T> void show(T a, int r, int l) { for (int i = 0; i < r; ++i) show(a[i], l); cout << endl; }
const double eps = 1e-9;
typedef double weight;
class graph_c
{
public:
void init(int _n);
void dijkstra(int S);
void add_edge(int u, int v, weight w);
weight dist[maxn];
private:
int n;
vector <int> r[maxn];
vector <weight> e[maxn];
int pa[maxn];
multimap <weight, int> h;
};
void graph_c::init(int _n)
{
n = _n;
for (int i = 0; i < n; i++)
{
r[i].clear();
e[i].clear();
}
}
void graph_c::add_edge(int u, int v, weight w)
{
r[u].push_back(v);
e[u].push_back(w);
}
void graph_c::dijkstra(int S)
{
weight d, tmp;
int v;
multimap<weight, int>::iterator it;
h.clear();
for (int i = 0; i < n; i++) dist[i] = -1;
dist[S] = 0;
pa[S] = -1;
h.insert(multimap<weight, int>::value_type(0, S));
while (!h.empty())
{
it = h.begin();
v = it->second;
d = it->first;
h.erase(it);
for (int i = 0; i < r[v].size(); i++)
{
tmp = d + e[v][i];
int j = r[v][i];
if (dist[j] < 0 || tmp < dist[j])
{
dist[j] = tmp;
pa[j] = v;
h.insert(multimap<weight, int>::value_type(tmp, j));
}
}
}
}
typedef struct point_t
{
double x, y;
};
typedef struct line_seg_t
{
point_t s, e;
};
double dist(const point_t &a, const point_t &b)
{
return sqrt((a.x - b.x) * (a.x - b.x) + (a.y - b.y) * (a.y - b.y));
}
int dblcmp(double d)
{
if (abs(d) < eps) return 0;
return d > 0 ? 1 : -1;
}
double det(double x1, double y1, double x2, double y2)
{
return x1 * y2 - x2 * y1;
}
double cross(const point_t &a, const point_t &b, const point_t &c)
{
return det(b.x - a.x, b.y - a.y, c.x - a.x, c.y - a.y);
}
bool seg_intersect(const line_seg_t &a, const line_seg_t &b)
{
return (dblcmp(cross(a.s, b.s, b.e)) ^ dblcmp(cross(a.e, b.s, b.e))) == -2
&& (dblcmp(cross(b.s, a.s, a.e)) ^ dblcmp(cross(b.e, a.s, a.e))) == -2;
}
line_seg_t wall[100];
int cnt_wall;
point_t p[100];
int cnt_p;
graph_c g;
int main()
{
int n;
while (scanf("%d", &n), n != -1)
{
cnt_wall = 0;
cnt_p = 2;
p[0].x = 0.0;
p[0].y = 5.0;
p[1].x = 10.0;
p[1].y = 5.0;
for (int i = 0; i < n; i++)
{
double t1, t2, t3, t4, t5;
scanf("%lf%lf%lf%lf%lf", &t1, &t2, &t3, &t4, &t5);
point_t pp;
pp.x = t1;
pp.y = t2;
p[cnt_p++] = pp;
pp.y = t3;
p[cnt_p++] = pp;
pp.y = t4;
p[cnt_p++] = pp;
pp.y = t5;
p[cnt_p++] = pp;
line_seg_t t;
t.s.x = t1;
t.s.y = 0.0;
t.e.x = t1;
t.e.y = t2;
wall[cnt_wall++] = t;
t.s.x = t1;
t.s.y = t3;
t.e.x = t1;
t.e.y = t4;
wall[cnt_wall++] = t;
t.s.x = t1;
t.s.y = t5;
t.e.x = t1;
t.e.y = 10.0;
wall[cnt_wall++] = t;
}
g.init(cnt_p);
for (int i = 0; i < cnt_p; i++)
for (int j = i + 1; j < cnt_p; j++)
{
line_seg_t ls;
ls.s = p[i];
ls.e = p[j];
int flag = 1;
for (int k = 0; k < cnt_wall && flag; k++)
if (seg_intersect(ls, wall[k])) flag = 0;
if (flag)
{
g.add_edge(i, j, dist(p[i], p[j]));
g.add_edge(j, i, dist(p[i], p[j]));
}
}
g.dijkstra(0);
printf("%.2lf\n", g.dist[1]);
}
return 0;
}