bzoj2709

http://www.lydsy.com/JudgeOnline/problem.php?id=2709

可以看出s到e的最短路关于v单调不减

二分v做最短路好了

注意精度，要卡到1e-7

program bzoj2709;const    eps=1e-7;    zl:array [1..4,1..2] of longint=((1,0),(-1,0),(0,1),(0,-1));varp,l,v,s,e:double;    t,x,y,tot,sx,sy,ex,ey,r,c,i,j,k:longint;    dis:array [0..101,0..101] of double;    map:array [0..101,0..101] of char;    dl:array [0..1000001] of record                                        x,y:longint;                                        end;begin    readln(t);    while t>0 do        begin            dec(t);            readln(l,r,c);            for i:=0 to r+1 do                for j:=0 to c+1 do                    map[i,j]:='#';            for i:=1 to r do                begin                       for j:=1 to c do                        begin                            read(map[i,j]);                            if map[i,j]='S' then                                begin                                    sx:=i;                                    sy:=j;                                end;                            if map[i,j]='E' then                                begin                                    ex:=i;                                    ey:=j;                                end;                        end;                    readln;                end;            s:=0;            e:=10;            while abs(s-e)>eps do                begin                    v:=(s+e)/2;                    fillchar(dis,sizeof(dis),87);                    dl[0].x:=sx;                    dl[0].y:=sy;                    tot:=0;                    dis[sx,sy]:=0;                    i:=0;                    while i<=tot do                        begin                            for j:=1 to 4 do                                begin                                    if j<=2 then p:=v                                                else p:=1;                                    x:=dl[i].x+zl[j,1];                                    y:=dl[i].y+zl[j,2];                                    if (map[x,y]<>'#')and(dis[x,y]>dis[dl[i].x,dl[i].y]+p) then                                        begin                                            dis[x,y]:=dis[dl[i].x,dl[i].y]+p;                                            inc(tot);                                            dl[tot].x:=x;                                            dl[tot].y:=y;                                        end;                                end;                            inc(i);                        end;                    if dis[ex,ey]<l then s:=v                                        else e:=v;                end;            writeln(s:0:5);        end;end.