POJ 1556 The Doors (线段相交+Dijkstra)

#include <cmath>
#include <cstdio>
/*
#include <iostream>  //不知道为什么加上这两句就报一些奇怪的错误····
using namespace std;
*/

#define MAX 500
#define eps 1e-8
#define INF 999999999999
#define zero(x) ( ((x) > 0 ? (x) : -(x)) < eps )

struct Point { double x, y;};
struct Line { Point a, b;};
Point point[MAX];
Line line[MAX];

double dis[MAX], edge[MAX][MAX];
bool vis[MAX];

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

bool oPointosite_side ( Point p1, Point p2, Point l1, Point l2 ) // 判断同侧或者异侧
{
return xmult(l1,p1,l2) * xmult(l1,p2,l2) < -eps;
}

bool intersect_ex ( Point u1, Point u2, Point v1, Point v2 ) // 判断是否相交
{
return oPointosite_side(u1,u2,v1,v2) && oPointosite_side(v1,v2,u1,u2);
}

double distance ( Point p1, Point p2 ) // 求两点间的距离
{
return sqrt((p1.x-p2.x)*(p1.x-p2.x) + (p1.y-p2.y)*(p1.y-p2.y));
}

bool check ( int lnum, Point p1, Point p2 )  // 对于任意两个点i,j，枚举所有的边，若它不与任意边相交，则返回true
{
for ( int i = 1; i <= lnum; i++ )
{
if ( intersect_ex ( p1, p2, line[i].a, line[i].b ) )
return false;
}
return true;
}

void build_map ( int pnum, int lnum )
{
int i, j;
for ( i = 0; i < pnum; i++ )
for ( j = i + 1; j <= pnum; j++ )
edge[i][j] = edge[j][i] = INF;

for ( i = 0; i < pnum; i++ )
{
for ( j = i + 1; j <= pnum; j++ )
if ( check ( lnum, point[i], point[j] ) ) // 若 i, j 之间没有墙壁阻挡，则可连一条边
edge[i][j] = edge[j][i] = distance ( point[i], point[j] );
}
}

double Dijkstra ( int pnum )
{
int i, j, k;
for ( i = 0; i <= pnum; i++ )
{
dis[i] = edge[0][i];
vis[i] = 0;
}
vis[0] = true;
dis[0] = 0;
for ( i = 1; i <= pnum; i++ )
{
double minc = INF;
for ( j = 0; j <= pnum; j++ )
{
if ( ! vis[j] && minc > dis[j] )
{
minc = dis[j];
k = j;
}
}
if ( minc == INF ) break;
vis[k] = true;
dis[k] = minc;
for ( j = 0; j <= pnum; j++ )
{
if ( ! vis[j] && dis[j] > dis[k] + edge[k][j] )
dis[j] = dis[k] + edge[k][j];
}
}
return dis[pnum];
}

int main()
{
int n;
while ( scanf("%d",&n) )
{
if ( n == -1 ) break;
double x, y1, y2, y3, y4;
int i, p = 0, l = 0;
point[0].x = 0; point[0].y = 5; // 0 为起点

for ( i = 1; i <= n; i++ )
{
scanf("%lf %lf %lf %lf %lf", &x, &y1, &y2, &y3, &y4 );
l++;
line[l].a.x = line[l].b.x = x;
line[l].a.y = 0; line[l].b.y = y1;
l++;
line[l].a.x = line[l].b.x = x;
line[l].a.y = y2; line[l].b.y = y3;
l++;
line[l].a.x = line[l].b.x = x;
line[l].a.y = y4; line[l].b.y = 10;

p++;
point[p].x = x; point[p].y = y1;
p++;
point[p].x = x; point[p].y = y2;
p++;
point[p].x = x; point[p].y = y3;
p++;
point[p].x = x; point[p].y = y4;
}
p++;
point[p].x = 10; point[p].y = 5; // p 为终点
build_map ( p, l );
double res = Dijkstra ( p );
printf("%.2lf\n",res);
}
return 0;
}