Gym - 100851F - Froggy Ford（dijkstra）

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <vector>
#include <ctype.h>
#include <queue>
using namespace std;
const int maxn=1e3+10;
const int inf=0x3f3f3f3f;
const int mod=1e9+7;
typedef long long ll;

struct point{
    double x,y;
    void read(){
        scanf("%lf%lf",&x,&y);
    }
    double operator ^(const point& rhs){
        return sqrt((x-rhs.x)*(x-rhs.x)+(y-rhs.y)*(y-rhs.y));
    }
}a[maxn];

struct Edge{
    int v,nxt;
    double dis;
}e[maxn*maxn*4];

int head[maxn],tot;
void init(){
    memset(head,-1,sizeof(head));
    tot=0;
}

void inline addEdge(int u,int v,double dis){
    e[tot]=Edge{v,head[u],dis},head[u]=tot++;
    e[tot]=Edge{u,head[v],dis},head[v]=tot++;
}

double dis[2][maxn];
int n,w;
struct node{
    int u;
    double md;
    bool used;
    point p;
    bool operator < (const node&rhs) const {
        return md>rhs.md||(md==rhs.md&& used>rhs.used);
    }
};

void diji(){
    for(int i=0;i<=n+1;i++) dis[0][i]=dis[1][i]=inf;
    priority_queue<node> q;
    q.push(node{0,0,false,point{0,0}});
    dis[0][0]=0;
    while(!q.empty()){
        node t=q.top();
        q.pop();
        int u=t.u;
        if(u==n+1){
            printf("%.6f %.6f\n",t.p.x,t.p.y);
            return;
        }
        for(int i=head[u];~i;i=e[i].nxt){
            int v=e[i].v;
            if(v==0) continue;
            if(t.used){
                if(dis[1][v]>max(t.md,e[i].dis)){
                    dis[1][v]=max(t.md,e[i].dis);
                    q.push(node{v,dis[1][v],true,t.p});
                }
            }else{
                double x,y;
                if(u!=0&&v!=n+1){
                    x=(a[u].x+a[v].x)/2.0;
                    y=(a[u].y+a[v].y)/2.0;
                }
                if(u==0&&v!=n+1){
                    x=a[v].x/2.0;
                    y=a[v].y;
                }
                if(u!=0&&v==n+1){
                    x=(w+a[u].x)/2.0;
                    y=a[u].y;
                }
                if(u==0&&v==n+1){
                    x=w/2.0;
                    y=0;
                }
                if(dis[0][v]>max(t.md,e[i].dis)){
                    dis[0][v]=max(t.md,e[i].dis);
                    q.push(node{v,dis[0][v],false,point{0,0}});
                }
                if(dis[1][v]>max(t.md,e[i].dis/2.0)){
                    dis[1][v]=max(t.md,e[i].dis/2.0);
                    q.push(node{v,dis[1][v],true,point{x,y}});
                }
            }
        }
    }
}


int main(){
#ifdef LOCAL
    freopen("in.txt","r",stdin);
#endif
    freopen("froggy.in","r",stdin);
    freopen("froggy.out","w",stdout);
    scanf("%d%d",&w,&n);
    for(int i=1;i<=n;i++) a[i].read();
    init();
    int vs=0,vt=n+1;
    addEdge(vs,vt,w);
    for(int i=1;i<=n;i++){
        addEdge(vs,i,a[i].x);
        addEdge(i,vt,w-a[i].x);
        for(int j=i+1;j<=n;j++)
            addEdge(i,j,a[i]^a[j]);
    }
    if(n==0){
        printf("%.6f 0.000000\n",w/2.0);
    }
    else diji();

    return 0;
}