NOIP复习-005——最短路

NUM.ONE——dijkstra单源最短路

var a:array[1..100,1..100]of longint;
    i,j,k,l,m,n,max,maxp:longint;
    dist:array[1..100]of longint;
    v:array[1..1000]of boolean;
begin
  readln(n);
  for i:=1 to n do
    for j:=1 to n do
     begin
      read(a[i,j]);
      if a[i,j]=0 then
        a[i,j]:=maxlongint;
     end;
  for i:=1 to n do
    dist[i]:=a[1,i];
  fillchar(v,sizeof(v),true);
  v[1]:=false;
  max:=maxlongint;
for k:=1 to n-1 do
  begin
  for i:=2 to n do
    if (a[1,i]and(v[i]) then
      begin
        max:=a[1,i];
        maxp:=i;
      end;
  v[maxp]:=false;
    for j:=1 to n do
      if v[j] then
        if a[maxp,j]then
       if dist[j]>dist[maxp]+a[maxp,j] then
         dist[j]:=dist[maxp]+a[maxp,j];
 end;
  for i:=1 to n do
    write(dist[i],' ');
end.

NUM.TWO——bellman ford算法

var a:array[1..1000,1..100]of longint;
    d:array[1..1000]of longint;
    i,j,k,l,m,n:longint;
    change:boolean;
begin
  readln(n);
  for i:=1 to n do
    for j:=1 to n do
      begin
        read(a[i,j]);
        if a[i,j]=0 then
          a[i,j]:=maxlongint;
      end;
  for i:=1 to n do
    d[i]:=a[1,i];
  for l:=1 to n-1 do
    for i:=1 to n do
      for j:=1 to n do
        if a[i,j]<>maxlongint then
          if d[j]<>maxlongint then
            if d[i]>d[j]+a[i,j] then
              d[i]:=d[j]+a[i,j];
  change:=true;
  for i:=1 to n do
    for j:=1 to n do
      if d[i]>d[j]+a[i,j] then
        begin
          change:=false;
          writeln('not possible');
          halt;
        end;
  for i:=1 to n do
    write(d[i],' ');
  end.

NUM.THREE——SPFA

var a,b:array[1..1000,0..100]of longint;
    d,dist:array[1..1000]of longint;
    v:array[1..1000]of boolean;
    c:array[1..100,1..100]of boolean;
    i,j,k,l,m,n:longint;
    head,tail:longint;
procedure spfa;
var i,j,k,l,m,now:longint;
begin
  fillchar(d,sizeof(d),0);
  fillchar(v,sizeof(v),false);
  for i:=1 to n do
    dist[i]:=maxlongint;
  dist[1]:=0;
  v[1]:=true;
  head:=1;
  tail:=1;
  d[1]:=1;
  while head<=tail do
    begin
      now:=d[head];
      for i:=1 to b[now,0]do
        if (dist[now]<>maxlongint) and (a[now,b[now,i]]<>maxlongint) then
        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]];
             if not v[b[now,i]] then
               begin
                 inc(tail);
                 d[tail]:=b[now,i];
                 v[b[now,i]]:=true;
               end;
          end;
      v[now]:=false;
      inc(head);
    end;
end;
begin
  readln(n);
  fillchar(b,sizeof(b),0);
  fillchar(c,sizeof(c),true);
  for i:=1 to n do
    for j:=1 to n do
      begin
        read(a[i,j]);
        if a[i,j]=0 then
          a[i,j]:=maxlongint;
        if a[i,j]<>maxlongint then
          if c[i,j] then
          begin
           c[j,i]:=false;
           c[i,j]:=false;
           inc(b[i,0]);
           b[i,b[i,0]]:=j;
           inc(b[j,0]);
           b[j,b[j,0]]:=i;
          end;
      end;
  spfa;
  for i:=1 to n do
    write(dist[i],' ');
end.