pku1674 Sorting by Swapping

这道题需要涉及到置换群的知识，只需知道一个定理。

最小交换次数=元素个数-环的个数。

View Code

 1 program pku1674(input,output);
 2 var
 3     number :array[0..11000] of integer;
 4     v       :array[0..11000] of boolean;
 5     n,cases:longint;
 6     answer :longint;
 7 procedure init;
 8 var
 9     i:longint;
10 begin
11     readln(n);
12     for i:=1 to n do
13         read(number[i]);
14     fillchar(v,sizeof(v),false);
15 end;{ init }
16 procedure main;
17 var
18     now,i:longint;
19 begin
20     answer:=0;
21     for i:=1 to n do
22     if not v[i] then
23     begin
24         inc(answer);
25         v[i]:=true;
26         now:=number[i];
27         while not v[now] do
28         begin
29             v[now]:=true;
30             now:=number[now];
31         end;
32     end;
33 end;{ main }
34 procedure print;
35 begin
36     writeln(n-answer);
37 end;{ print }
38 begin
39     readln(cases);
40     while cases>0 do
41     begin
42         dec(cases);
43         init;
44         main;
45         print;
46     end;
47 end.