pku3617 Best Cow Line

有一个字符串，每次只能从两端取，求取得的字典序最小的子符序列。

每次比较剩余字符串的正向和反向字符串的大小，正向大就在尾取，否则在头取，相当于贪心了吧。

View Code

 1 program pku3617(input,output);
 2 var
 3    s1,s2  : ansistring;
 4    answer : ansistring;
 5    n      : longint;
 6 procedure init;
 7 var
 8    i  : longint;
 9    ch : char;
10 begin
11    readln(n);
12    s1:='';
13    for i:=1 to n do
14    begin
15       readln(ch);
16       s1:=s1+ch;
17    end;
18    s2:='';
19    for i:=length(s1) downto 1 do
20       s2:=s2+s1[i];
21 end; { init }
22 procedure main;
23 var
24    i : longint;
25 begin
26    answer:='';
27    for i:=1 to n do
28    begin
29       if s1>s2 then
30       begin
31      answer:=answer+s2[1];
32      delete(s2,1,1);
33      delete(s1,length(s1),1);
34       end
35       else
36       begin
37      answer:=answer+s1[1];
38      delete(s1,1,1);
39      delete(s2,length(s2),1);
40       end;
41    end;
42 end; { main }
43 procedure print;
44 var
45    tmp : ansistring;
46 begin
47    while length(answer)>=80 do
48    begin
49       tmp:=copy(answer,1,80);
50       writeln(tmp);
51       delete(answer,1,80);
52    end;
53    if answer<>'' then
54       writeln(answer);
55 end; { print }
56 begin
57    init;
58    main;
59    print;
60 end.