如何检查字符串是否包含2个相同字符

def check_duplicate_chars(string):
    for i in range(len(string)):
        for j in range(i + 1, len(string)):
            if string[i] == string[j]:
                return True
    return False

def check_duplicate_chars(string):
    return len(set(string)) < len(string)

def check_duplicate_chars(string):
    counter = [0] * 26
    for char in string:
        index = ord(char) - ord('a')
        counter[index] += 1
        if counter[index] > 1:
            return True
    return False