Submission #132451

#	Time	Username	Problem	Language	Result	Execution time	Memory
132451		duality	Fences (JOI18_fences)	C++11	100 / 100	843 ms	4540 KiB

fences

#include <bits/stdc++.h>
using namespace std;
#define mp make_pair
#define pb push_back
typedef long long int LLI;
typedef vector<int> vi;
typedef pair<int,int> pii;
typedef vector<pii> vpii;
#define x first
#define y second
#define point pair<double,double>
#define EPS 1e-9

struct seg { point a,b; };
seg s[104];
bool comp(point a,point b) {
    return (abs(a.x-b.x) < EPS) && (abs(a.y-b.y) < EPS);
}
bool comp2(point a,point b) {
    if (abs(a.x-b.x) < EPS) return a.y < b.y-EPS;
    else return a.x < b.x;
}
int ccw(point a,point b,point c) {
    return (b.x-a.x)*(c.y-a.y) > (b.y-a.y)*(c.x-a.x)+EPS;
}
int coll(point a,point b,point c) {
    return abs((b.x-a.x)*(c.y-a.y)-(b.y-a.y)*(c.x-a.x)) < EPS;
}
point closest(point p,seg s) {
    if (s.a == s.b) return s.a;
    point a = s.a,b = s.b;
    point ap = mp(p.x-a.x,p.y-a.y),ab = mp(b.x-a.x,b.y-a.y);
    double f = (ap.x*ab.x+ap.y*ab.y)/(ab.x*ab.x+ab.y*ab.y);
    if (f < 0) return a;
    if (f > 1) return b;
    return mp((1-f)*a.x+f*b.x,(1-f)*a.y+f*b.y);
}
int onSeg(point p,seg s) {
    return comp(closest(p,s),p);
}
int inter(point a,point b,point c,point d) {
    if (coll(a,b,c) || coll(a,b,d) || coll(c,d,a) || coll(c,d,b)) return 0;
    else return (ccw(a,b,d) != ccw(a,b,c)) && (ccw(c,d,a) != ccw(c,d,b));
}
point points[22000];
int check(point a,point b,int S) {
    if ((a.x > -S+EPS) && (a.x < S-EPS) && (a.y > -S+EPS) && (a.y < S-EPS)) return 0;
    if ((b.x > -S+EPS) && (b.x < S-EPS) && (b.y > -S+EPS) && (b.y < S-EPS)) return 0;
    point c = (point){(1-1e-6)*a.x+1e-6*b.x,(1-1e-6)*a.y+1e-6*b.y};
    if ((c.x > -S+EPS) && (c.x < S-EPS) && (c.y > -S+EPS) && (c.y < S-EPS)) return 0;
    c = (point){(1-1e-6)*b.x+1e-6*a.x,(1-1e-6)*b.y+1e-6*a.y};
    if ((c.x > -S+EPS) && (c.x < S-EPS) && (c.y > -S+EPS) && (c.y < S-EPS)) return 0;
    if (onSeg(mp(0,0),(seg){a,b})) return 0;
    if (inter(a,b,mp(S,S),mp(S,-S))) return 0;
    if (inter(a,b,mp(S,-S),mp(-S,-S))) return 0;
    if (inter(a,b,mp(-S,-S),mp(-S,S))) return 0;
    if (inter(a,b,mp(-S,S),mp(S,S))) return 0;
    return 1;
}
vector<pair<int,double> > adjList[44000];
int addEdge(point a,point b,int N,int c,int S,int f) {
    int u = lower_bound(points,points+c,a,comp2)-points;
    int v = lower_bound(points,points+c,b,comp2)-points;
    if (check(a,b,S)) {
        double d = f ? 0:sqrt((a.x-b.x)*(a.x-b.x)+(a.y-b.y)*(a.y-b.y));
        if (inter(a,b,mp(0,0),mp(1e9,1))) {
            adjList[2*u].pb(mp(2*v+1,d)),adjList[2*u+1].pb(mp(2*v,d));
            adjList[2*v].pb(mp(2*u+1,d)),adjList[2*v+1].pb(mp(2*u,d));
        }
        else {
            adjList[2*u].pb(mp(2*v,d)),adjList[2*u+1].pb(mp(2*v+1,d));
            adjList[2*v].pb(mp(2*u,d)),adjList[2*v+1].pb(mp(2*u+1,d));
        }
    }
    return 0;
}
double dist[44000];
priority_queue<pair<double,int> > H;
double findDist(int s,int c) {
    int i;
    for (i = 0; i < 2*c; i++) dist[i] = 1e99;
    dist[2*s] = 0,H.push(mp(0,2*s));
    while (!H.empty()) {
        int u = H.top().second;
        double d = -H.top().first;
        H.pop();

        if (d > dist[u]) continue;
        for (i = 0; i < adjList[u].size(); i++) {
            int v = adjList[u][i].first;
            if (d+adjList[u][i].second < dist[v]) {
                dist[v] = d+adjList[u][i].second;
                H.push(mp(-dist[v],v));
            }
        }
    }
    return dist[2*s+1];
}
int main() {
    int i;
    int N,S;
    scanf("%d %d",&N,&S);
    for (i = 0; i < N; i++) scanf("%lf %lf %lf %lf",&s[i].a.x,&s[i].a.y,&s[i].b.x,&s[i].b.y);
    s[N] = (seg){mp(S,S),mp(S,S)};
    s[N+1] = (seg){mp(S,-S),mp(S,-S)};
    s[N+2] = (seg){mp(-S,S),mp(-S,S)};
    s[N+3] = (seg){mp(-S,-S),mp(-S,-S)};
    N += 4;

    int j,c = 0;
    for (i = 0; i < N; i++) {
        for (j = 0; j < N; j++) points[c++] = closest(s[i].a,s[j]),points[c++] = closest(s[i].b,s[j]);
    }
    sort(points,points+c,comp2);
    c = unique(points,points+c,comp)-points;
    for (i = 0; i < N; i++) {
        for (j = 0; j < N; j++) {
            if (i != j) {
                addEdge(s[i].a,closest(s[i].a,s[j]),N,c,S,0);
                addEdge(s[i].b,closest(s[i].b,s[j]),N,c,S,0);
            }
        }
    }
    for (i = 0; i < N; i++) {
        for (j = 0; j < c; j++) {
            if (onSeg(points[j],s[i])) addEdge(points[j],s[i].a,N,c,S,1);
        }
    }
    double ans = 1e99;
    for (i = 0; i < N; i++) {
        ans = min(ans,findDist(lower_bound(points,points+c,s[i].a,comp2)-points,c));
        ans = min(ans,findDist(lower_bound(points,points+c,s[i].b,comp2)-points,c));
    }
    printf("%.10lf\n",ans);

    return 0;
}

Compilation message (stderr)

fences.cpp: In function 'double findDist(int, int)':
fences.cpp:89:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
         for (i = 0; i < adjList[u].size(); i++) {
                     ~~^~~~~~~~~~~~~~~~~~~
fences.cpp: In function 'int main()':
fences.cpp:102:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d %d",&N,&S);
     ~~~~~^~~~~~~~~~~~~~~
fences.cpp:103:34: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     for (i = 0; i < N; i++) scanf("%lf %lf %lf %lf",&s[i].a.x,&s[i].a.y,&s[i].b.x,&s[i].b.y);
                             ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 18 / 18
• Subtask 2: 33 / 33
• Subtask 3: 49 / 49