[二分][记搜]JZOJ 3522 迷宫花园

#include <iostream>
#include <cstdio>
#include <queue>
#include <cmath>
using namespace std;
const int N=110;
struct Point {
    int x,y;
}s,e;
int dx[4]={0,1,0,-1},dy[4]={1,0,-1,0};
double f[N][N];
char ch[N][N];
int t,r,c;
double l,v;
bool inqueue[N][N];

double Cost(Point a,Point b) {
    if (abs(a.y-b.y)==1) return 1.0;
    else return v;
}

bool Judge(Point a,Point b) {
    if (b.x<1||b.x>r||b.y<1||b.y>c) return 0;
    if (ch[b.x][b.y]==‘#‘) return 0;
    if (f[a.x][a.y]+Cost(a,b)>f[b.x][b.y]) return 0;
    return 1;
}

void Bfs()  {
    queue<Point> q;
    while (!q.empty()) q.pop();
    for (int i=1;i<=r;i++)
        for (int j=1;j<=c;j++)
            f[i][j]=2147483647.0;
    q.push(s);f[s.x][s.y]=0;inqueue[s.x][s.y]=1;
    while (!q.empty()) {
        Point p=q.front();q.pop();
        for (int i=0;i<4;i++)
            if (Judge(p,(Point){p.x+dx[i],p.y+dy[i]})) {
                Point to=(Point){p.x+dx[i],p.y+dy[i]};
                f[to.x][to.y]=f[p.x][p.y]+Cost(p,to);
                if (!inqueue[to.x][to.y]) q.push(to);
                inqueue[to.x][to.y]=1;
            }
        inqueue[p.x][p.y]=0;
    }
}

int main() {
    freopen("maze.in","r",stdin);
    freopen("maze.out","w",stdout);
    scanf("%d",&t);
    for (;t;t--) {
        scanf("%lf%d%d",&l,&r,&c);
        for (int i=1;i<=r;i++)
            for (int j=1;j<=c;j++) {
                do {
                    scanf("%c",&ch[i][j]);
                }
                while (ch[i][j]!=‘#‘&&ch[i][j]!=‘E‘&&ch[i][j]!=‘S‘&&ch[i][j]!=‘ ‘);
                if (ch[i][j]==‘E‘) e.x=i,e.y=j;
                if (ch[i][j]==‘S‘) s.x=i,s.y=j;
            }
        double ll=1e-7,rr=10.0;
        while (rr-ll>=1e-7) {
            v=(ll+rr)/2.0;
            Bfs();
            if (f[e.x][e.y]<l) ll=v+1e-7;
            else rr=v;
        }
        printf("%.5lf\n",v);
    }
}