Codechef•Jun 09, 2025

Complementary Strand in a DNA

Hazrat Ali

Codechef

You are given the sequence of Nucleotides of one strand of DNA through a string SS of length NN. SS contains the character A,T,C,A,T,C, and GG only.

Chef knows that:

  • AA is complementary to TT.
  • TT is complementary to AA.
  • CC is complementary to GG.
  • GG is complementary to CC.

Using the string SS, determine the sequence of the complementary strand of the DNA.

Input Format

  • First line will contain TT, number of test cases. Then the test cases follow.
  • First line of each test case contains an integer NN - denoting the length of string SS.
  • Second line contains NN characters denoting the string SS.

Output Format

For each test case, output the string containing NN characters - sequence of nucleotides of the complementary strand.

Constraints

  • 1≤T≤100
  • 1≤N≤100
  • SS contains A, T, C, and G only

Sample 1:

Input 
4
4
ATCG
4
GTCC
5
AAAAA
3
TAC
 
Output
TAGC
CAGG
TTTTT
ATG


Solution

t = int(input())
for _ in range(t):
    n = int(input())
    strand = input()
    complement = ''

    for ch in strand:
        if ch == 'A':
            complement += 'T'
        elif ch == 'T':
            complement += 'A'
        elif ch == 'C':
            complement += 'G'
        else:  # ch == 'G'
            complement += 'C'

    print(complement)






 

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