Complementing a Strand of DNA

In DNA strings, symbols 'A' and 'T' arecomplements of each other, as are 'C' and 'G'.

The reverse complement of a DNA string s isthe string sc formed by reversing the symbols of s, then taking the complementof each symbol (e.g., the reverse complement of "GTCA" is"TGAC").

Given: A DNA string s of length at most1000 bp.

Return: The reverse complement sc of s.

Sample Dataset

AAAACCCGGT

Sample Output

ACCGGGTTTT

针对以上案例，我准备了三种解答方案：

#!/usr/bin/python

s='AAAACCCGGT'

b= s[::-1]  #步长为-1的序列

c="" # 空字符串

for i in b:

  if i=='A':

    c=c+'T' #  +号代表连接作用

 elif i=='T':

    c=c+'A'

 elif i=='C':

    c=c+'G'

 else:

    c=c+'C'

print c

第二种办法 利用字母的大小写差异：

#!/usr/bin/python

s='AAAACCCGGT'

complement_AT=s.replace("A","t")

complement_TA=complement_AT.replace("T","a")

complement_GC=complement_TA.replace("G","c")

complement_CG=complement_GC.replace("C","g")

complement_dna=complement_CG.upper() #转换成大写字母

reverse_complement_dna=complement_dna[::-1]

print s

print reverse_complement_dna

第三种办法：

利用字典键值对应的办法：

#!/usr/bin/python

s='AAAACCCGGT'

b= s[::-1]

c=[]

complement_dna={"A":"t","T":"a","C":"g","G":"c"}

for i in b:

  c.append(complement_dna[i].upper()) #利用字典的键得到值，并且转换成大写字母

print s

print "".join(c)  #列表连接成字符串且中间不带有任何空格