poj 1556 线段相交 + dijstra

code :

#include <cstdio>#include <cmath>#include <vector>#include <cstring>using namespace std;typedef double ld;const ld eps = 1e-13;int n;ld dis[75][75], ans[75];ld x, d, md, mu, u;bool vis[75];struct Point {    ld x, y;    Point(ld _x, ld _y) : x(_x), y(_y) {};    Point operator - (const Point &rhs) const {        return Point(x - rhs.x, y - rhs.y);    }    ld lenth() {        return sqrt(x * x + y * y);    }    ld operator * (const Point &rhs) {        return x * rhs.y - y * rhs.x;    }    friend ld len(Point &a, Point &b) {        return (a - b).lenth();    }};struct Line {    Point s, e;    Line(Point _s, Point _e) : s(_s), e(_e) {};};vector<Point> vec;vector<Line>  vLine;int ok(ld a) {    if (a > eps) return 1;    return fabs(a) < eps ? 0 : -1;}bool check(Line a, Line b) {    ld l = (a.s - b.s) * (a.e - b.s), r = (a.s - b.e) * (a.e - b.e);    ld u = (b.s - a.s) * (b.e - a.s), d = (b.s - a.e) * (b.e - a.e);    return ok(l) * ok(r) >= 0 || ok(u) * ok(d) >= 0;}void solve() {    for (int i = 0; i < vec.size(); ++i) {        for (int j = i + 1; j < vec.size(); ++j) {            if (fabs(vec[i].x - vec[j].x) < eps) continue;            dis[i][j] = 51;            bool f = 1;            for (int k = 0; k < vLine.size(); ++k) {                if (!check(Line(vec[i], vec[j]), vLine[k])) {                    f = 0;                    break;                }            }            if (f) dis[i][j] = len(vec[i], vec[j]);        }    }    //printf("mid\n");    memset(vis, 0, sizeof vis);    for (int i = 1; i < vec.size(); ++i)ans[i] = dis[0][i];    //vis[0] = 1;    ans[0] = 0;    for (int i = 0; i < vec.size(); ++i) {        //printf("s\n");        int u;        ld mn = 51;        for (int j = 0; j < vec.size(); ++j) {            if (!vis[j] && ans[j] < mn) {                mn = ans[j];                u = j;            }        }            vis[u] = 1;             for (int j = 0; j < vec.size(); ++j) {                if (!vis[j] && (ans[u] + dis[u][j] < ans[j])) {                    ans[j] = ans[u] + dis[u][j];                }            }    }    printf("%.2lf\n", ans[vec.size() - 1]);}int main() {    while (~scanf("%d", &n), ~n) {        vec.clear();        vLine.clear();        vec.push_back(Point(0, 5));        //printf("1\n");        for (int i = 1; i < 4 * n + 1; i += 4) {            scanf("%lf%lf%lf%lf%lf", &x, &d, &md, &mu, &u);            //printf("%lf %lf\n", x, d);            vec.push_back(Point(x, d));            vec.push_back(Point(x, md));            vec.push_back(Point(x, mu));            vec.push_back(Point(x, u));            dis[i][i + 1] = dis[i + 1][i] = md - d;            dis[i][i + 2] = dis[i + 2][i] = dis[i][i + 3] = dis[i + 3][i] = 50;            dis[i + 1][i + 2] = dis[i + 1][i + 3] = dis[i + 2][i + 1] = dis[i + 3][i + 1] = 50;            dis[i + 2][i + 3] = dis[i + 3][i + 2] = u - mu;            vLine.push_back(Line(Point(x, 0), Point(x, d)));            vLine.push_back(Line(Point(x, md), Point(x, mu)));            vLine.push_back(Line(Point(x, u), Point(x, 10)));        }        vec.push_back(Point(10, 5));        //printf("111\n");        solve();    }    return 0;}