APIO '08 P3 - DNA
View as PDFOne interesting use of computers is to analyze biological data such as DNA sequences. Biologically,
a strand of DNA is a chain of nucleotides Adenine, Cytosine, Guanine, and Thymine. The four
nucleotides are represented by characters A, C, G, and T, respectively. Thus, a strand of DNA can be
represented by a string of these four characters. We call such a string a DNA sequence.
It is possible that the biologists cannot determine some nucleotides in a DNA strand. In such
a case, the character N is used to represent an unknown nucleotide in the DNA sequence of the
strand. In other words, N is a wildcard character for any one character among A, C, G or T. We
call a DNA sequence with one or more character N an incomplete sequence; otherwise, it is called a
complete sequence. A complete sequence is said to agree with an incomplete sequence if it is a result of
substituting each N in the incomplete sequence with one of the four nucleotides. For example, ACCCT
agrees with ACNNT, but AGGAT does not.
Researchers often order the four nucleotides the way we order the English alphabets: A comes before
C, C comes before G, G comes before T. A DNA sequence is classified as form- if every nucleotide in
it is the same as or comes before the nucleotides immediately to its right. For example,
AACCGT is
form-, but
AACGTC is not.
In general, a sequence is form-, for
, if it is a form-(
) or it is a concatenation of a
form-(
) sequence and a form-
sequence. For example,
AACCC, ACACC, and ACACA are form-, but
GCACAC and ACACACA are not.
Again, researchers order DNA sequences lexicographically the way we order words in a dictionary.
As such, the first form- sequence of length
is
AAAAA, and the last is TTTTT. As another example,
consider the incomplete sequence ACANNCNNG. The first seven form- sequences that agree with it are:
Task
Write a program to find the th form-
sequence that agrees with the given incomplete sequence of
length
.
Input
The first line contains three integers separated by one space:
,
,
and
. The second line contains a string of length
, which is the incomplete
sequence. It is guaranteed that the number of form-
sequences that agree with the incomplete
sequence is not greater than
. Moreover,
does not exceed the number of form-
sequences that agree with the
given incomplete sequence.
Output
On the first line, print the th form-
sequence that agrees with the incomplete sequence in the
input.
Sample Input 1
9 3 5
ACANNCNNG
Sample Output 1
ACAAACCCG
Sample Input 2
5 4 10
ACANN
Sample Output 2
ACAGC
Scoring
The score for each input scenario will be if the correct answer is outputted and
otherwise.
In test scenarios worth points,
will be at most
.
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