题解 | DNA序列

s = input()
n = int(input())
data = {}
for i in range(len(s)-n+1):
    _s = s[i:i+n]
    percent = (_s.count("C") + _s.count("G"))/len(s)
    data.setdefault(percent, []).append(_s)
data = sorted(data.items(), key=lambda x: x[0], reverse=True)
print(data[0][1][0])