我们先二分一个答案,对于每个答案,先加一级公路,如果不够k直接break,
然后再加二级公路,加的过程类似Kruskal。
/************************************************************** Problem: 1196 User: BLADEVIL Language: Pascal Result: Accepted Time:444 ms Memory:732 kb ****************************************************************/ //By BLADEVIL var n, m, k :longint; pre1, succ1, c1, c2 :array[0..20010] of longint; pre2, succ2 :array[0..20010] of longint; father :array[0..10010] of longint; ans :longint; procedure swap(var a,b:longint); var c :longint; begin c:=a; a:=b; b:=c; end; procedure qs1(low,high:longint); var i, j, xx :longint; begin i:=low; j:=high; xx:=c1[(i+j) div 2]; while i<j do begin while c1[i]<xx do inc(i); while c1[j]>xx do dec(j); if i<=j then begin swap(pre1[i],pre1[j]); swap(succ1[i],succ1[j]); swap(c1[i],c1[j]); inc(i); dec(j); end; end; if i<high then qs1(i,high); if j>low then qs1(low,j); end; procedure qs2(low,high:longint); var i, j, xx :longint; begin i:=low; j:=high; xx:=c2[(i+j) div 2]; while i<j do begin while c2[i]<xx do inc(i); while c2[j]>xx do dec(j); if i<=j then begin swap(pre2[i],pre2[j]); swap(succ2[i],succ2[j]); swap(c2[i],c2[j]); inc(i); dec(j); end; end; if i<high then qs2(i,high); if j>low then qs2(low,j); end; procedure init; var i :longint; begin read(n,k,m); for i:=1 to m-1 do begin read(pre1[i],succ1[i],c1[i],c2[i]); pre2[i]:=pre1[i]; succ2[i]:=succ1[i]; end; qs1(1,m-1); qs2(1,m-1); end; function getfather(x:longint):longint; begin if father[x]=x then exit(x); father[x]:=getfather(father[x]); exit(father[x]); end; procedure main; var l, r, mid :longint; i :longint; fa, fb, a, b :longint; cnt :longint; begin l:=1; r:=30000; while l<=r do begin mid:=(l+r) div 2; cnt:=0; for i:=1 to n do father[i]:=i; for i:=1 to m-1 do begin if c1[i]>mid then break; a:=pre1[i]; b:=succ1[i]; fa:=getfather(a); fb:=getfather(b); if fa<>fb then begin father[fa]:=fb; inc(cnt); end; end; for i:=1 to m-1 do begin if (cnt<k) or (c2[i]>mid) then break; a:=pre2[i]; b:=succ2[i]; fa:=getfather(a); fb:=getfather(b); if fa<>fb then begin father[fa]:=fb; inc(cnt); end; end; if cnt<n-1 then l:=mid+1 else begin ans:=mid; r:=mid-1; end; end; writeln(ans); end; begin init; main; end.