[Vijos1082 丛林探险]

[题目来源]：vijos1082

[关键字]：最短路

[题目大意]：n个点m条边k的体力，每条边有一个长度和一个费体力值，能否从st走到ed，若能走到则最短走多少。

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[分析]：就是用spfa求一遍最短路，只是在松弛时要加上一条：如果走此边不会耗费超过k的体力。至于图的存储结构，可以用邻接表或前向星。

[代码]：

View Code

  1 type
  2   rec = record
  3     x, y, d1, d2: longint;
  4   end;
  5 var
  6   n, m, st, ed, limit: longint;
  7   e: array[0..90000] of rec;
  8   l, r: array[0..6000] of longint;
  9   d1, d2: array[0..6000] of longint;
 10   b: array[0..6000] of boolean;
 11   q: array[0..500000] of longint;
 12 
 13 procedure qs(l, r: longint);
 14 var
 15   i, j, mid, mid2: longint;
 16   t: rec;
 17 begin
 18   i := l;
 19   j := r;
 20   mid := l+random(r-l+1);
 21   mid2 := e[mid].y;
 22   mid := e[mid].x;
 23   repeat
 24     while (e[i].x < mid) or ((e[i].x = mid) and (e[i].y < mid2)) do inc(i);
 25     while (e[j].x > mid) or ((e[j].x = mid) and (e[j].y > mid2)) do dec(j);
 26     if i <= j then
 27       begin
 28         t := e[i];
 29         e[i] := e[j];
 30         e[j] := t;
 31         inc(i);
 32         dec(j);
 33       end;
 34   until i > j;
 35   if l < j then qs(l,j);
 36   if i < r then qs(i,r);
 37 end;
 38 
 39 procedure init;
 40 var
 41   i, x, t: longint;
 42 begin
 43   readln(n,m);
 44   t := 0;
 45   for i := 1 to m do
 46     begin
 47       readln(e[i].x,e[i].y,e[i].d1,e[i].d2);
 48       inc(t);
 49       e[m+t].x := e[i].y;
 50       e[m+t].y := e[i].x;
 51       e[m+t].d1 := e[i].d1;
 52       e[m+t].d2 := e[i].d2;
 53     end;
 54   readln(st,ed);
 55   readln(limit);
 56   randomize;
 57   qs(1,2*m);
 58   for i := 1 to 2*m do
 59     begin
 60       x := e[i].x;
 61       if l[x] = 0 then l[x] := i;
 62       r[x] := i;
 63     end;
 64   //for i := 1 to n do writeln(l[i],'',r[i]);
 65 end;
 66 
 67 procedure spfa;
 68 var
 69   h, t, i, x: longint;
 70 begin
 71   h := 1;
 72   t := 1;
 73   q[1] := st;
 74   fillchar(b,sizeof(b),false);
 75   b[st] := true;
 76   fillchar(d1,sizeof(d1),0);
 77   d1[st] := 0;
 78   fillchar(d2,sizeof(d2),100);
 79   d2[st] := 0;
 80   while h <= t do
 81     begin
 82       x := q[h];
 83       for i := l[x] to r[x] do
 84         if (d1[x]+e[i].d1 <= limit) and (d2[x]+e[i].d2 < d2[e[i].y]) then
 85           begin
 86             d2[e[i].y] := d2[x]+e[i].d2;
 87             d1[e[i].y] := d1[x]+e[i].d1;
 88             if not b[e[i].y] then
 89               begin
 90                 inc(t);
 91                 q[t] := e[i].y;
 92                 b[e[i].y] := true;
 93               end;
 94           end;
 95       b[x] := false;
 96       inc(h);
 97     end;
 98   if d2[ed] <> d2[0] then writeln(d2[ed]) else writeln(-1);
 99 end;
100 
101 begin
102   assign(input,'d:\1.in');reset(input);
103   assign(output,'d:\1.out');rewrite(output);
104   init;
105   spfa;
106   close(input);
107   close(output);
108 end.