isValidTrafficSequence.py

print("Implemented by Pedro Izecksohn.")

def isValidTrafficSequence (seq):
    if not seq:
        return True
    i=0
    while i<(len(seq)-1):
        i+=1
        if seq[i-1]=="red":
            if seq[i]=="green":
                continue
            return False
        if seq[i-1]=="yellow":
            if seq[i]=="red":
                continue
            return False
        if seq[i-1]=="green":
            if seq[i]=="yellow":
                continue
            return False
        print("Invalid data.")
        exit()
    return True

def main():
    seq=[]
    s="a"
    while len(s):
        s=input()
        if len(s):
            seq.append(s)
    print(isValidTrafficSequence(seq))

if __name__=="__main__":
    main()