统计输入的小写英文字符的出现频率。

program BubbleSorter;
var
        n, i, j : integer;
        t : char;
        st : array[1 .. 100] of char;
        noswap : boolean;
begin
        readln(n);
        for i := 1 to n do
                read(st[i]);
        for i := 1 to n do
        begin
                noswap := true;
                for j := 1 to n-i do
                        if st[j] > st[j+1] then
                        begin
                                t := st[j];
                                st[j] := st[j+1];
                                st[j+1] := t;
                                noswap := false;
                        end;
                if (noswap) then break;
        end;
        for i := 1 to n do
                write(st[i]);
        writeln;
        t := char(0);
        for i := 1 to n do
                if st[i] = t then
                        j := j+1
                else
                begin
                        if i <> 1 then
                           writeln(st[i-1], '  ', j);
                        j := 1;
                        t := st[i];
                end;
        writeln(st[i], '  ', j);
        readln;
        readln;
end.


program SortStatisticser;
var
        n, i : integer;
        j : char;
        st : array[1 .. 100] of char;
        ch : array['a' .. 'z'] of integer;
begin
        readln(n);
        for i := 1 to n do
        begin
                read(st[i]);
                ch[st[i]] := ch[st[i]] + 1;
        end;
        for j := 'a' to 'z' do
                for i := 1 to ch[j] do
                    write(j);
        writeln;
        for j := 'a' to 'z' do
                if ch[j] <> 0 then
                    writeln(j, '  ', ch[j]);
        readln;
        readln;
end.