SPFA

const

maxp=10000; {最大结点数}

var {变量定义}

p,c,s,t:longint; {p,结点数;c,边数;s:起点;t:终点}

a,b:array[1..maxp,0..maxp] of longint; {a[x,y]存x,y之间边的权;b[x,c]存与x相连的第c个边的另一个结点y}

d:array[1..maxp] of integer; {队列}

v:array[1..maxp] of boolean; {是否入队的标记}

dist:array[1..maxp] of longint; {到起点的最短路}

head,tail:longint; {队首/队尾指针}

procedure init;

var

i,x,y,z:longint;

begin

r ead(p,c);

for i := 1 to c do

begin

r eadln(x,y,z); {x,y:一条边的两个结点;z:这条边的权值}

inc(b[x,0]); b[x,b[x,0]] := y; a[x,y] := z; {b[x,0]：以x为一个结点的边的条数}

inc(b[y,0]); b[y,b[y,0]] := x; a[y,x] := z;

end;

r eadln(s,t); {读入起点与终点}

end;

pr ocedur e spfa(s:longint); ｛SPFA｝

var

i,,j,now,sum:longint;

begin

fillchar(d,sizeof(d),0);

fillchar(v,s izeof(v),false);

for j := 1 to p do dist[ j ]:=max longint;

dist[s] := 0; v[s] := true; d[1] := s; {队列的初始状态,s为起点}

head := 1; tail := 1;

w hile head<=tail do {队列不空}

begin

now:= d[head]; {取队首元素}

for i := 1 to b[now,0] do

if dist[b[now,i]]>dist[now]+a[now,b[now,i]] then

begin

dist[b[now,i]]:= dist[now]+a[now,b[now,i]]; {修改最短路} if not v[b[now,i]] then {扩展结点入队}

begin

inc(tail);

d[tail] := b[now,i];

v[b[now,i]] := true;

end;

end;

v[now] := false; {释放结点}

inc(head); {出队}

end;

end;

pr ocedur e pr int;

begin

w riteln(dist[t]);

end;

begin

init;

spfa(s);

pr int;

end.