题解 | 好串

def main():
    s = input()
    st = 0
    n = len(s)
    for i in range(n):
        if s[i] == 'a':
            st += 1
        elif s[i] == 'b':
            if st == 0:
                print("Bad")
                return
            st -= 1
    if st != 0:
        print("Bad")
        return
    print("Good")

if __name__ == "__main__":
    main()

栈的思想