[USACO 4.4.1 Shuttle Puzzle]

[题目来源]：USACO 4.4.1

[关键字]：数学

[题目大意]：一个1*2n+1的棋盘，左边有n个白子，中间一个空格，右边n个黑子，求出将其交换的步骤。

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[分析]：http://www.nocow.cn/index.php/USACO/shuttle

[代码]：

View Code

 1 {
 2 ID:x yr;
 3 PROB:shuttle
 4 LANG:PASCAL
 5 }
 6 var
 7   n, s: longint;
 8   a: array[0..200] of longint;
 9 
10 procedure init;
11 var
12   i, c: longint;
13 begin
14   readln(n);
15   s := 4;
16   i := 1;
17   c := 5;
18   while i < n do
19     begin
20       s := s+c;
21       inc(i);
22       inc(c,2);
23     end;
24   //writeln(s);
25   //readln;
26 end;
27 
28 procedure work;
29 var
30   i, l, c1, c2: longint;
31 begin
32   i := 1;
33   l := 1;
34   c1 := -1;
35   c2 := 2;
36   while i <= s div 2 do
37     begin
38       a[i] := c1;
39       for i := i+1 to i+l do
40         a[i] := c2;
41       inc(l);
42       c1 := -c1;
43       c2 := -c2;
44       inc(i);
45     end;
46   c1 := 0;
47   l := s div 2;
48   if not odd(n) then begin inc(l); inc(c1); end;
49   for i := l to s do
50     begin
51       a[i] := a[i-c1];
52       inc(c1,2);
53     end;
54   //for i := 1 to s do write(a[i],'');
55   //readln;
56   l := n+1;
57   for i := 1 to s-2 do
58     begin
59       l := l+a[i];
60       if i mod 20 = 0 then writeln(l) else write(l,'');
61     end;
62   l := l+a[s-1];
63   writeln(l);
64   //readln;
65 end;
66 
67 begin
68   assign(input,'shuttle.in');reset(input);
69   assign(output,'shuttle.out');rewrite(output);
70   init;
71   work;
72   close(input);
73   close(output);
74 end.