OJ-Problems-Source/HDOJ/4077_autoAC.cpp
2016-09-04 14:21:47 +08:00

113 lines
3.2 KiB
C++

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <algorithm>
#include <functional>
#include <vector>
#include <map>
#include <cstring>
#include <string>
#include <list>
#include <set>
#include <bitset>
#include <cctype>
#include <cmath>
#include <ctime>
#include <numeric>
#include <utility>
#include <stack>
#include <queue>
#include <deque>
#include <iomanip>
#include <cassert>
#define pb push_back
#define mp make_pair
#define Maxn 1100
#define fi first
#define se second
using namespace std;
typedef pair<double, double> pii;
const double eps=1e-8;
const double inf=1e300;
int n;
double dp[Maxn][2];
pii seg[Maxn][2];
inline double getdis(pii a, pii b)
{
return sqrt((a.fi-b.fi)*(a.fi-b.fi)+(a.se-b.se)*(a.se-b.se));
}
inline int sign(double x)
{
return x<-eps?-1:x>eps;
}
pii intersert(pii A, pii B, double y)
{
double dx = A.fi - B.fi;
double dy = A.se - B.se;
return mp(A.fi + (y-A.se)*dx/dy, y);
}
bool leftturn(pii p, pii a, pii b)
{
double x1 = (a.fi-p.fi), y1 = (a.se-p.se);
double x2 = (b.fi - p.fi), y2 = (b.se-p.se);
return sign(x1*y2-x2*y1)>0;
}
bool noRightTurn(pii p, pii a, pii b)
{
double x1 = (a.fi-p.fi), y1 = (a.se-p.se);
double x2 = (b.fi - p.fi), y2 = (b.se-p.se);
return sign(x1*y2 - x2*y1)>=0;
}
int main()
{
double a, b, c;
while (~scanf("%d", &n), n)
{
scanf("%lf%lf", &a, &b);
seg[0][0] = mp(a, b);
for (int i=1; i<=n; i++)
{
scanf("%lf%lf%lf", &c, &a, &b);
seg[i][0] = mp(a, c);
seg[i][1] = mp(b, c);
}
dp[n][0] = dp[n][1] = 0;
int j;
for (int i=n-1; i>=0; i--)
{
for (int side=0; side<2; side++)
{
dp[i][side] = inf;
pair<pii,pii> next = mp(seg[i+1][0], seg[i+1][1]);
pii pt = seg[i][side];
for (j=i+1; j<=n; j++)
{
if (leftturn(pt, seg[j][1], next.fi) || leftturn(pt, next.se, seg[j][0])) break;
if (noRightTurn(pt, next.fi, seg[j][0]))
{
next.fi = seg[j][0];
dp[i][side] = min(dp[i][side], getdis(pt, next.fi)+dp[j][0]);
}
if (noRightTurn(pt, seg[j][1], next.se))
{
next.se = seg[j][1];
dp[i][side] = min(dp[i][side], getdis(pt, next.se)+dp[j][1]);
}
}
if (j > n)
{
double y = seg[n][0].se;
next.fi = intersert(pt, next.fi,y);
next.se = intersert(pt, next.se, y);
if (pt.fi < next.fi.fi) dp[i][side] = min(dp[i][side], getdis(pt, next.fi));
else if (pt.fi > next.se.fi) dp[i][side] = min(dp[i][side], getdis(pt, next.se));
else dp[i][side] = min(dp[i][side], pt.se - y);
}
if (i == 0) break;
}
}
printf("%.10f\n", dp[0][0]);
}
return 0;
}